The invention discloses a designing method for a pressure reducing structure of a high-parameter multi-stage pressure reducing valve with pore plates. The method is applicable to designing of the high-parameter multi-stage pressure reducing valve with a valve element and the pore plates as the main body throttling components. The designing method comprises the steps that the critical pressure ratio Vcr of media is calculated; the pressure reducing stage of the multi-stage pressure reducing valve with the pore plates is calculated; the pressure ratio v of each stage of throttling component is calculated; the inlet pressure Pj of the jth stage of pore plate is calculated; the flowing sectional areas of the valve element at different flow opening degrees are calculated; the flowing sectional area of each pore plate under the maximum flow is calculated; and the actual pressure reducing ratio of all the stages of throttling components is detected through a finite element method. Reasonable given parameter designing of the high-parameter multi-stage pressure reducing valve can be achieved, especially under the high pressure ratio condition, the pressure ratios of steam before and behind the throttling components are greater than the critical pressure ratio, supersonic flow is prevented from occurring in the pressure reducing valve, turbulent dissipation and exergy loss of fluid in the multi-stage pressure reducing valve are reduced, and the valve is more energy-saving, safe and stable.