The invention discloses an anti-loosening method for a valve deck of a drilling pump. Depending on an adjustable anti-loosening device, the anti-loosening method comprises the steps that first, a retaining disk is mounted on the valve deck; second, the adjustable anti-loosening device is assembled; third, a push rod is adjusted to tightly press the retaining disk; fourth, a locking steel wire is led out from rectangular holes from an ejection screw to the two sides of the rear portion of a swing pressing block, so that the ejection screw is subjected to anti-loosening fixation. According to the method, anti-loosening is conduced on the valve deck of a hydraulic cylinder, due to the fact that a mechanical anti-loosening method is adopted, a valve deck thread can be effectively prevented from loosening under the condition that the drilling pump operates, the phenomenon that a valve plug sealing ring leaks due to the looseness of the valve deck is effectively avoided, and the operating reliability of the drilling pump is improved.