Displacement stepped output device of mud pump in managed pressure drilling and application method of displacement stepped output device

The invention relates to the technical field of managed pressure drilling, in particular to a displacement stepped output device of a mud pump in managed pressure drilling and an application method of the displacement stepped output device. The displacement stepped output device comprises a liquid inlet pipe, an adjusting pipe, a setting module and a logic judgement module, wherein the liquid inlet pipe is fixed with the adjusting pipe through a tee joint, a flow monitoring module and a first switch valve are fixedly mounted on the liquid inlet tube, and a second switch valve and a throttling valve are sequentially fixedly mounted on the adjusting pipe. The displacement stepped output device has the advantages that during managed pressure drilling, the displacement of a mechanical pump can be input into a shaft in a stepped manner during the starting and stopping processes of the pump, so that an automatic throttling manifold can have sufficient time to supplement well bottom pressure change caused by pump starting and stopping, the well bottom pressure is kept constant during pump starting and stopping, and technical support is provided for the implementation of the managed pressure drilling technology.