The invention relates to a liquid solid separating method for regenerating filtrate medium in filter, comprising the steps of: separating liquid solid two phases, removing filter cake, removing the filtrate medium and replacing the filtrate medium. Suspending liquid which is to be separated and includes fine solid grain is pumped into a novel quick opening type pressure leaf filter; under the function of the pressure of the pump, the solid phase grain is intercepted on the surface of the filtrate medium so as to form the filter cake; and the filtrate liquid passes through the filter cake and the filtrate medium and enters into the centre pipe of a filtrate disc so as to be discharged after being gathered. After the step of separating, a rotate positioning device drives a filter element to be rotated at an uniform speed, high-pressure water disassembles and cleans the filter cake which is covered on the filtrate medium by a nuzzle, and the filtrate medium is regenerated. The step of replacing the filtrate medium is carried out by fast switching the filter by a pneumatic control quick opening device. Compared with the prior art, the invention has the advantages of reasonable structure, safe operation, high work efficiency, high equipment automation degree, less management and maintenance workload, safe use, wide application range, etc.