Provided is a fan blowback valve. The problems that dust and powder are easily adsorbed on an existing agricultural machine, and the product cooling performance is affected are solved. The hydraulic system comprises a reversing valve, a pressure compensator, a main oil inlet, a first oil return port, a first working oil port and a second working oil port, the second working oil port is connected with a fan blade control mechanism; the reversing valve is provided with a first position for disconnecting the main oil inlet from the second working oil port and a second position for communicating the main oil inlet with the second working oil port; the pressure compensator comprises a first opening, a second opening, a third opening and a fourth opening; and pressure oil at the fourth port is communicated with the first control cavity to open the pressure compensator, so that the fourth port is communicated with the second working oil port through the third port, and the first oil port receives the pressure oil at the main oil inlet and is communicated with the first working oil port through the second port. The utility model also has the advantages of simple structure, convenience in assembly, reliable action, long service life and the like.