Based on the entrance throttle control system of series-connecting governor valve, the mathematic model was set up with load as input and pressure of hydraulic cylinder chamber without rod as output. The system was simplified as stable second-order system, and the changing rules of pressure over-shooting were obtained. The pressure sensor was applied to the pressure measurement in the hydraulic cylinder chamber without rod, especially the pressure over-shooting. The conclusions of theoretical derivation and analysis were verified through tests .