A structure for opening a grip cover of a toy gun includes a bottom cover assembly and a rear cover assembly. The bottom cover assembly has a bottom cover covering a bottom surface of the grip and a pivot penetrating the grip and the bottom cover. One end of the bottom cover adjacent to the pivot is formed with a first hook. The rear cover assembly has a rear cover covering a rear surface of the grip. The rear cover has a protrusion connected to the grip. One end of the rear cover away from the protrusion is formed with a second hook to be engaged with the first hook. With this structure, the first hook is separated from the second hook when the bottom cover rotates downwards, thereby driving the rear cover to open rearwards by using the protrusion as a center of rotation. In this way, by only opening the bottom cover, the user can open the rear cover assembly simultaneously, thereby exchanging a pressurized gas cylinder in the grip more rapidly. Further, the problem that members may get lost or suffer damage can be prevented.