The invention provides a four-axis unmanned aerial vehicle for water quality detection. The four-axis unmanned aerial vehicle for water quality detection comprises an unmanned aerial vehicle body, vehicle arms, a control device and a water storage box. The vehicle arms are connected with the unmanned aerial vehicle body, and a rotating motor is arranged on every vehicle arm and is in driving connection with a screw propeller. The control device comprises a CPU master chip, a power module, an electromagnetic valve control module, a water pump, a distance-measuring sensor and a power supply, wherein the power module, the electromagnetic valve control module, the water pump, the distance-measuring sensor and the power supply are connected with the CPU master chip, and the power module is connected with every motor. The water storage box is divided into at least two water storage layers, a connecting tube is connected to every water storage layer and is connected with the water pump, an electromagnetic valve is arranged between the water pump and every connecting tube, and the electromagnetic valve control module is connected with the electromagnetic valves. The four-axis unmanned aerial vehicle for water quality detection can acquire water quality data at precise positions and is simple in structure and capable of guaranteeing gravity center stability after sampling.