The invention provides a hydraulic system for controlling a tail gate of a pavement milling machine. The hydraulic system comprises an overflow valve, an electromagnetic overflow valve, a first two-position four-way electromagnetic reversing valve, a second two-position four-way electromagnetic reversing valve, a first normally-closed two-position two-way electromagnetic reversing ball valve, a second normally-closed two-position two-way electromagnetic reversing ball valve, a three-position four-way electromagnetic reversing valve, a conveying motor of a belt conveyor, a fixed pressure reducing valve and a tail gate lifting oil cylinder. The hydraulic system has the advantages that the technical scheme is adopted, so that the operating quality of the milling machine is improved, the energy consumption is reduced, the performance is reliable, the structure is simple, the cost is cheap, lifting, locking, floating and back pressure functions of the tail gate can be achieved, the whole weight of the tail gate and a conveying device is grounded, pressure oil is fed into a rod cavity of the tail gate lifting oil cylinder to reduce the ground pressing of the tail gate, the ground pressing can be adjusted according to pavement conditions, the construction quality is guaranteed, the energy consumption is effectively reduced, and the operation is convenient.