A gear checked construction for a toy gun comprises a gun body, a piston, a driving gear, and a check assembly. The piston is mounted inside the gun body and a rack is formed on the bottom of the piston. The driving gear engages with the rack to drive the piston and includes a clamping part. The check assembly comprises a hinge and a check bar. The hinge is mounted inside the gun body and the check bar is set around the hinge and comprises a forward part and a reverse part. The clamping part touches on the forward part and bursts through the check bar when the driving gear rotates in one direction to drive the piston, and the clamping part engages with the reverse part to stop the driving gear's rotation when the driving gear rotates in the other direction.