In this paper,a kind of design method of the unloading unit is creatively advanced that is used for generating large value and wide frequengcy range negative step force.

A new standard negative step force device, which is recently developed and used for large force value (up to 1200kN) and wide frequency band (highest analyzing frequency is 50kHz) force transducer′s calibration, is introduced in this paper.

Use the throttle speed governing system with by-pass oil way in which the hydraulic cylinder was the executive as research object in this thesis , the trial research about the effect on the pressure p1 of the hydraulic cylinder chamber without piston-rod when series-connecting throttle or timing valve on the by-pass oil way under the step load changing have made.

Used the metering-out control system in which the hydraulic cylinder was the executive element as research object in this thesis, the experimental research about the effect on the pressure P1, P2 of the hydraulic cylinder chambers when series-connecting throttle valve or governor valve on the return oil-line under the step load changing have made.

The rise time of one kind of negative step force measurement is introduced,by affixing the thin leads along two side of the test bar,the broken time delay between the top side and the base side is obtained,and the rise time of the negative step force is gained.