The invention provides a system for measuring the flowing speed of steam in flowing channels, and belongs to the technical field of steam flowing speed measuring. The system is composed of a differential pressure measuring device, a gas clearing device and a steam physical property parameter compensation device; a pitot tube is sequentially connected with a high-pressure pressure guiding tube, a high-pressure valve of a five-valve set, and the high-pressure side of a differential pressure transmitter; a low-pressure pressure guiding tube is sequentially connected with a low-pressure valve of the five-valve set and the low-pressure side of the differential pressure transmitter; a high-pressure inert gas device is sequentially connected with an adjusting valve, a gas-water removing device, acheck valve and a verifying valve of the five-valve set; and the steam physical property parameter compensation device is composed of a thermocouple and a pressure transmitter. According to the system, the pressure loss in the measuring process is small, the measuring error caused by liquid evaporation in the pressure guiding tubes in the measuring process can be avoided, a physical property parameter correction system is arranged, and thus the flowing speed of the steam in the different flowing channels can be accurately measured under the situation of not causing the large pressure loss.