A multi-channel ultrasonic flowmeter includes transducer assemblies (21, 22,23, 24) and a pipe housing (10). Four transducer assembly installation holes (9) arranged at two ends of the pipe housing (10) close to flanges (4). The transducer assemblies (21, 22, 23, 24) are provided in the installation holes (9). The transducer assemblies (21, 22, 23, 24) includes transducers (7) and stationary posts (1). An upper portion of the stationary post (1) has a first cylindrical body (109). A lower portion of the stationary post (1) has a flat key-shaped protrusion (105) extending in an axial direction. The flat key-shaped position-limiting protrusion (105) limits rotation of the stationary post (1) around an axial thereof, and ensures accurate positioning of the axis of the stationary post (1). The transducer (7) and the stationary post (1) are respectively sealed to prevent leakage of a fluid. The multi-channel ultrasonic flow meter provides a thorough solution about fixed installation, positioning and sealing of the transducer (7), has a compact structure, can be installed conveniently, and has good sealing performance.