The invention discloses a purified water filling process for a water injection cylinder for a urinary catheterization bag. The purified water filling process comprises the following steps that (1) sterile purified water is prepared, specifically, newly-prepared purified water is selected, a conical flask is filled with the newly-prepared purified water and then put in a high-pressure steam sterilizer, sterilization treatment is conducted, and the sterile purified water is prepared; (2) treatment before filling is conducted, specifically, a 100-grade operation clean table is selected in a purified workshop, and the empty water injection cylinder and the sterile purified water are put on the 100-grade operation clean table; (3) filling is conducted, specifically, the empty water injection cylinder is filled with the sterile purified water, and during filling, 9 cm nutrient agar culture dishes are placed on the left side, the middle and the right side of the 100-grade operation clean table correspondingly; and (4) detecting after filling is conducted, specifically, after filling, the culture dishes placed in the step (3) are sent to a testing laboratory and detected according to regulations, so that whether filling is conducted in a sterile environment or not is judged. The process is concise in working procedure, easy to operate, full in sterilization and capable of effectively guaranteeing sterile filling of the purified water.