In 1952, Melicow first proposed the concept of bladder carcinoma in situ, which refers to intraepithelial carcinoma confined within the mucosal layer only, i.e., not infiltrating and not growing exophytically into the bladder lumen, with the characteristics of high grade and low stage. Clinically, bladder carcinoma in situ can be divided into three types, the first one is primary bladder carcinoma in situ, which is mostly diagnosed by positive tumor cells in urine exfoliation cell examination or abnormal bladder mucosa in cystoscopy, taking biopsy and random biopsy; the second one is secondary bladder carcinoma in situ, which is found in situ during postoperative follow-up of bladder tumor; the third one is concomitant carcinoma in situ, also called paraneoplastic carcinoma in situ, which is mostly found in normal or abnormal mucosa around solid bladder carcinoma. The third type of associated carcinoma in situ, also called paraneoplastic carcinoma in situ, is mostly found in the normal or abnormal mucosa surrounding the solid bladder cancer.