Abstract: The present disclosure provides a multi-layer open channel portable flow measuring device based on a water impulse principle and a flow measuring method; an instantaneous water head height of a water-carrying section, namely, a water level H is measured through a pressure sensor at a bottom of a U-shaped hollow tube; at the same time, layered multi-point velocity measuring components in equidistant layout include a series of position “current meters” composed of tension sensors, hollow punching lightweight steel balls and lightweight elastic steel ropes to measure velocities V1-n of different points, n depends on the layer decided to be arranged according to a channel depth, an instantaneous flow value of the whole water-carrying section is further acquired through multi-layer flow accumulation, and with a simple structure, intelligent control, easy operation and convenient carrying, the present disclosure may further improve the flow measuring precision.