If urination sometimes hurts and sometimes does not, then the possible causes are: 1. Chronic infection of the urinary system, so that it can appear when it hurts and sometimes does not. If the pain increases during the acute exacerbation of chronic infection, but does not occur during the recovery period or only a slight pain, it may be accompanied by frequent urination and urinary urgency, and further urinalysis is needed to further clarify; 2. Stones in the urinary system, such as bladder stones and urethral stones, produce pain in the process of discharge, but do not produce pain during the resting period. Sometimes it may be accompanied by bleeding and obstruction of urination, which requires ultrasound examination of the urinary system to confirm the diagnosis; 3. Tumors, polyps and other lesions of the urinary tract can have pain when combined with chronic infections. When the infection is healed, but the tumor polyp is not completely cured, there may be slight pain or no pain at this time, and further ultrasound and cystoscopy of the urinary system are needed to confirm the diagnosis.