The hardened mass of blood vessels under the left testicle may be caused by varicocele, which can be categorized into primary and secondary, and the patient should consult a doctor in time. 1. Primary varicocele: varicocele can be caused by missing or dysfunctional spermatic vein valves, hypoplasia of the levator ani muscle, and weak connective tissue around the spermatic cord. Patients will have hardened mass-like blood vessels under the testicles, accompanied by a feeling of swelling, which can be relieved when lying down and resting, preferably on the left side, such people should maintain a light diet, and if necessary, can be localized cold compresses or surgical treatment. 2. Secondary varicocele: caused by abdominal tumor, renal tumor, hydronephrosis and other peripheral lesions compressing the spermatic vein, patients will also have a hard mass of blood vessels under the left testicle. And it does not disappear when lying down, and it should be treated for the primary disease that causes varicose veins. If the patient finds the hardened mass of blood vessels under the left testicle, he should consult the doctor in time to clarify the cause of the disease, and be treated under the guidance of the doctor.