A hydraulic control clamping and overturning system for large-power diesel engine cylinder cover air valve assembling comprises a hydraulic supply loop, a hydraulic motor control mechanism, a hydraulic arm clamping mechanism and a hydraulic cylinder stroke control mechanism. The hydraulic supply loop comprises an oil tank, a flow meter, an oil injection filter, a filter with a pressure meter and aspring check valve, a motor, a hydraulic pump, the pressure meter, a pressure reduction safety valve and a two-position two-way electromagnetic valve. The hydraulic motor control mechanism comprisesa three-position four-way electromagnetic valve, a mutual control type double hydraulic control one-way valve, a pressure reduction safety valve and a hydraulic motor. The hydraulic arm clamping mechanism comprises a three-position four-way electromagnetic valve, a mutual control type double hydraulic control one-way valve, a duplex one-way speed adjusting valve, a pressure accumulator, a stop valve capable of being opened and closed, a pressure reduction safety valve, a plunger hydraulic cylinder and a pressure relay, and the plunger hydraulic cylinder is provided with a hydraulic arm. The hydraulic cylinder stroke control mechanism comprises a three-position four-way electromagnetic valve, a mutual control type double hydraulic control one-way valve, a one-way speed adjusting valve withelectromagnetic releasing, a pressure relay and a plunger hydraulic cylinder. The hydraulic control clamping and overturning system is high in automation degree and functionality, the operation efficiency is improved, the installing precision is improved, and safety and stability are achieved.