The invention discloses a method for improving sensitivity of a piezoresistive sensor based on a fragmented structure. Particularly, the fragmented structure is introduced into the piezoresistive sensor, wherein the resistance which corresponds with the fragmented structure can change when the pressure condition of the piezoresistive sensor changes, thereby generating an additional change of the resistance of piezoresistive sensor when the pressure condition of the piezoresistive sensor changes. The fragmented structure is formed through stacking a plurality of fragmented porous materials. According to the method of the invention, through improving key active material structures of the piezoresistive sensor and the like, the fragmented structure is introduced into the piezoresistive sensor, thereby increasing the variable resistance of a sample to an external pressure, and further obtaining a simple and applicable method for increasing PRS and a preparation method of a corresponding piezoresistive pressure sensor. Compared with prior art, the method of the invention can effectively settle a problem of incapability of detecting low pressure by the PRS.