Rhabdomyosarcoma is a common soft tissue malignancy and is a fast-growing, highly malignant tumor. It is more common in children and less common in adults, and its incidence accounts for 5% to 8% of pediatric solid malignancies and more than half of soft tissue sarcomas in childhood. It can develop in all age groups of pediatric patients, and the two peak incidence periods are 2-4 years old and 15-17 years old. The prevalent sites reported in the literature are, in order of preference, the head and face, neck and genitourinary tract, extremities, trunk and posterior peritoneum. Transverse myxosarcoma in the perineum presents as a widespread, diffuse mass with indistinct boundaries, normal or grayish skin color, insignificant pain, no significant pressure or fluctuating sensation, and a firm, fixed texture. If complicated by infection, there may be redness, swelling and heat. At the later stage, the surface is ulcerated, erosion, pus and filth, with foul smell. If the tumor invades the rectum, there is difficulty in defecation, and if it invades the vagina or urethra, there is difficulty in urination or vaginal discharge, etc. The early clinical symptoms of perianal rhabdomyosarcoma are very similar to those of perianal abscess, but the redness, swelling and pain are not obvious, and there is no or may be accompanied by fever, which is often misdiagnosed. Clinically, if atypical perianal abscess is found in the perianal area; redness, swelling, heat and pain; symptoms are not obvious, and the mass is extensive and hard, the disease should be highly suspected. The only means of definite diagnosis is to take histopathological examination, and if it is not detected at one time, deep histopathological examination can be repeated several times. The etiology of this disease is not fully understood, but it is generally believed to be due to abnormal embryonic development. Rhabdomyosarcoma is formed by rhabdomyosarcoma cells with different degrees of differentiation and originates from rhabdomyoblasts or undifferentiated mesenchymal tissue. The tumor is widely distributed, occurring in various organs of the body where the rhabdomyosarcoma is distributed, or in areas where the rhabdomyosarcoma is not distributed. There are four histological types: pleomorphic, glandular, embryonic and chylomicron. Glandular rhabdomyosarcoma has small, blister-like cells with few central cells. Grapevine rhabdomyosarcoma is seen underneath the intact mucosal migrating epithelium and consists of several layers of short spindle-shaped cells parallel to the mucosa; neoplastic layer;. In pediatric rhabdomyosarcoma, there is a predominance of embryonic type with varying degrees of differentiation of tumor cells. microscopically, it is common to see a moderate number of smaller tumor cells scattered in a sparse mucinous or edematous background, and nuclear division is rare. the tumor forms a mass in the soft tissue with an oval, irregular or lobulated shape. a clear histologic definition of RMS was proposed by Stout in 1946. Specimens of rhabdomyosarcoma appear on light microscopy as consisting of characteristic striated muscle cells, with electron microscopy able to distinguish subtypes, and on immunohistochemistry as positive for intermediate filaments and undifferentiated muscle cell protein components (scaffolding proteins, myosin, actin and the transcription factor myoD). Treatment of rhabdomyosarcoma includes surgery, radiotherapy and chemotherapy, each of which plays a considerable role in survival rates. Surgery used to be the primary management of RMS until new chemotherapeutic agents became available. For tumors of limited scope, combined radical abdominoperineal resection could be pursued, while those with large scope could be treated with radiotherapy until the tumor shrinks and then surgically treated. However, clinical observation shows that the scope of the disease is wide and it is difficult to completely remove the tumor radically. In our three cases, the masses were all circumferential and reached both sides of the sciatic nodes externally, so radical surgery could not be done. Due to the high malignancy of rhabdomyosarcoma, the tumor is prone to recurrence despite the comprehensive treatment with radiation therapy, chemotherapy, ultrasonic focused knife and surgical resection. The disease has the tendency to spread locally in the early stage, and it can also spread to the lung and liver through the lymphatic system or bloodstream, so the prognosis is poor.