Abstract: A flow stopper preventing the backflow of urine comprises a urinary catheter connector, a flow stopping valve, and a urinary bag connector. The flow stopping valve is a membrane material. A flow channel runs through the front and rear ends of the flow stopping valve. The flow channel is provided with a front-end inlet and a rear-end outlet. The front-end inlet is in communication with a valve port of the urinary catheter connector. The rear-end outlet is a flat slit. A channel of the urinary bag connector is provided with a front-end port and a rear-end port connected to a tube of a urinary bag. The flow stopping valve is arranged within the channel. Moreover, the rear-end outlet of the flow channel faces the rear-end port of the channel. The flow stopper can prevent the backflow of the urine and prevent a patient from being infected.