The invention discloses a novel composite filter for blocking silt and particles smaller than the silt, belonging to the technical field of geothermal heating. The novel composite filter comprises a filter body, a first flow slowing plate, a second flow slowing plate, a sand removing mechanism, a water inlet pipe, a filtering unit, a water outlet pipe, a settling layer and a box door, wherein thewater inlet pipe is fixedly arranged on one side of the filter body, the water outlet pipe is fixedly arranged on the other side of the filter body, and the first flow slowing plate is movably arranged on the inner wall of the filter body. Through arrangement of the sand removing mechanism, the filter is enabled to settle micro-silt onto a sand guiding plate through the settling effect of the settling layer; after the filter is stopped, a baffle is pulled through an inserting block, and then the micro-silt is discharged through a silt discharging opening, so the filter effectively discharges the micro-silt filtered in the device and has a remarkable effect on particles which are difficult to treat in the centrifugal process of a cyclone desander, the high cost of a coarse filter and a precise filter can be saved, and the practicability of the filter is improved.