The invention provides an inner water-cooled generator stator anti-vapor blocking device which is connected with a stator waterway of a generator cooling system. The anti-vapor blocking device comprises a temperature measurement element, a flowmeter and a pressure release unit. The temperature measurement element is arranged at a 12-o'clock position of a parallel ring top end of the stator and used for predetermining occurrence of a vapor blocking phenomenon. The flowmeter is arranged on an outer wall of a small conflux pipe and used for predetermining occurrence of the vapor blocking phenomenon. A flow signal of the flowmeter and a measurement signal of the temperature measurement element are led outside the generator by a generator base box terminal and are jointly sent to a generator monitoring system. The pressure release unit is connected to the 12-o'clock position of the parallel ring top end of the stator through a pipe and used for releasing vapor-blocked gas. By monitoring temperature and water pressure of the parallel ring top end of the stator and the system flow, accidents that a stator coil is overheated and winding bars are burned due to vapor blocking of the generator can be timely and effectively prevented, and the equipment operation reliability is improved.