Abstract: An underwater launching apparatus for a small unmanned aerial vehicle capable of floating on water, having an airbag, inflating module, airbag arm, cylindrical body, upper baffle plate, spring, airbag arm connecting rod, lower baffle plate, upper buckle and lower buckle. This apparatus has compact and reliable structure. Relative to a traditional underwater catapult, the apparatus has smaller body and completes deployment and ejection of the launching apparatus by means of elasticity of the spring. The underwater launching apparatus for the small unmanned aerial vehicle has high stability and diversified applications. After the airbag arm of the catapult is deployed on the water and the inflating module inflates the airbag, developed area is larger and resistance to wind and waves is stronger. In a deployed state, a sensor on the unmanned aerial vehicle can be matched and steadily deployed on the water for investigation.