An unmanned water quality sampling and detecting system is provided for continuous and repeated detection and sampling in different depths and different areas for a long time, and comprises a drone, acontrol box, a pull wire and a sampling tube, wherein the control box is internally provided with a battery, a circuit control module, a lifting motor, a motor bracket and a reel; a sampling cylinderis particularly designed with uncovered top and conical bottom, and contains a sensor group, a water pressure gauge, a sealing motor and a sealing cover, and the water quality is sampled by controlling the sealing motor to open and close the sealing cover; at the same time, a core chip of a main control unit of the system uses a low-power device, and the main control unit detects the water depthdata of the water pressure gauge and controls the opening/closing of the sensor group, thereby greatly improving continuous working hours. Through the set of devices, the water quality can be on-linemeasured, recorded and automatically sampled several times in succession under different water depth conditions.