A water spray gun includes a main body, an operating member and a switch part. The main body includes a handle portion and a tube portion extended from the handle portion and provided with a spray head. A control assembly is enclosed in the main body for control of water outflow and adjustment of the amount of the water outflow. The operating member is pivotally connected to the position where the handle portion meets the tube portion. The switch part is arranged at the operating member and is engaged with the control assembly. The amount of water outflow is controlled by relative movement between the switch part and the operating member.