The invention discloses an underwater catapulting device which comprises a base, a shell and a catapult base. The shell and the catapult base are both installed on the base, a compressed air bottle is installed on the shell, a bottom column is installed at the center of the catapult base and fixedly connected with a pipe, a jacking column is installed at the top of the pipe, a shaft rod is installed in the pipe, the lower end of the shaft rod is connected with a piston located in the pipe, the upper end of the shaft rod penetrates through the jacking column to be connected with a catapult head, and the catapult head is connected with a small catapult ball. According to the underwater catapulting device, an underwater catapulting function is achieved by conducting waterproof treatment on the catapulting device, a variable-angle catapulting function is achieved through hinge connection and protractor indication, the method that catapulting power is supplied by an air compressor in a traditional catapult is changed, the test device can be applied to special experimental environments such as the closed experimental environment and the variable-pressure experimental environment by adopting the compressed air bottle through the mode of wirelessly controlling test starting and stopping, and the experimental requirements are better met.