The invention discloses an underwater rock crushing experimental device. The experimental device is characterized by comprising an experimental pool, and an experimental device is arranged in the experimental pool; the experimental device comprises a base with a lower end fixedly arranged at the bottom of the experimental pool, the middle of the base is hollow and a crushing experiment body is arranged at the pool bottom corresponding to the hollow location of the base; a fixed plate is further horizontally arranged on the base, a two-dimensional movement control mechanism is arranged betweenthe base and a fixed plate, and used for driving the fixed plate to move along a two-dimensional direction; multiple vertically and downwardly arranged telescopic mechanisms are horizontally distributed on the fixed plate, and the lower ends of the telescopic mechanisms are fixedly connected with crushing hammer devices; the telescopic mechanisms can drive the crushing hammer devices to verticallymove, so that working ends of the crushing hammer devices can be acted on the crushing experiment body. The invention further discloses an underwater rock crushing experimental method. The experimental device disclosed by the invention can perform crushing test by simulating the construction condition, the actual crushing construction successful rate and the efficiency are improved.