The invention discloses an automatic sampler of a water quality sampling UAV (Unmanned Aerial Vehicle). The automatic sampler comprises a main body support, a fixed height sensor, a water sample collecting device, a lifting device, a sample dividing device, a sample storage device and a control circuit board, wherein the water sample collecting device comprises a submersible pump, a pressure and liquid level sensor, a flexible water pipe and a flow sensor and is capable of completing fixed-depth sampling; the lifting device comprises a servo motor, a magnetic encoder, a reduction gear, a slip ring, a bearing, a proximity switch, a telescopic rod and a ceramic eye component and is capable of realizing retracing and releasing functions of the water sample collecting device; the sample storage device is formed by three layers of detachable plastic bottles. According to the automatic sampler disclosed by the invention, the weight of the automatic sampler can be effectively reduced, and the performance of the whole water quality sampling UAV is increased; meanwhile, the fixed-depth sampling is realized through the lifting device and the pressure and liquid level sensor which is additionally arranged in a sampling opening, the water quality collecting device can be retracted during a flying process of the water quality sampling UAV, and the safety during the flying process of the water quality sampling UAV is increased.