The invention discloses a submerging jet flow testing box and a testing method. The testing box includes a box body, jet flow water inlets, a vision window, a pressure gauge interface, a relief port, a clamp holder, a feeding device interface, a liquid stream valve port, a drainage port and the like. During the laboratory experiment process, a submerging fluid field environment is improved, and the approximate engineering practical submerging jet flow is simulated; other testing instrument is combined, the submerging jet flow fluid field structure is observed; the potential core of jet under the submerging condition is observed combined with a three dimensional laser particle imaging velocimeter (3DPIV) system; the variation of different jet nozzle jet flow fluid field structures is analyzed, and the internal structures of the jet nozzles are optimized; the accelerating mechanism and distribution condition of grinding material particles during the submerging grinding material jet flow testing are analyzed; and meanwhile, the observation experiment for cutting and flushing material under the submerging condition can be performed. The submerging jet flow testing box and the testing method have the advantages that the structure is simple, the operation is convenient, nozzles can be replaced easily, a plurality of testing functions are provided, and compared with other jet flow testing devices, the submerging jet flow testing box not only can test the jet flow fluid field structure under the submerging condition, but also can be reutilized repeatedly, thereby saving the experimental expense at the same time.