The utility model relates to a dirt-filtering piston type pressure-reducing valve which comprises a medium intake cavity, a medium exhaust cavity, a main valve cavity flow passage which sends the medium into the intake cavity and the exhaust cavity, a main piston cavity and an auxiliary valve cavity which are sequentially arranged above the medium exhaust cavity, a main valve which is mounted in the main valve cavity flow passage; wherein the top of the valve shaft of the main valve is connected with the main piston in the main cylinder, an auxiliary valve is mounted in the auxiliary valve cavity, a reset spring is provided at the bottom of the main valve clack, the upper part of the valve shaft of the auxiliary valve penetrates the center sealed shaft hole of the valve cavity to touch the metal film which is provided above, an adjusting spring and an adjusting screw are sequentially arranged above the metal film, the auxiliary valve cavity is communicated respectively with the medium intake cavity and the main piston cavity through a upper flow passage and a lower flow passage, the medium exhaust cavity is communicated with the cavity under the metal film through a flow passage, and a filtering cavity with a filter member is provided in the flow passage between the medium intake cavity and the auxiliary valve cavity.