The invention discloses a method for quantitatively characterizing the shale compressibility based on rock physics. The method comprises the following steps: (1) establishing a shale compressibility mathematical model; (2) analyzing the relationship between formation parameters and mechanics, and preferably selecting formation mechanical parameter characterizing factors; (3) regressively fitting a compressive strength elastic parameter characterization formula and establishing a formation fracture pressure elastic parameter characterization formula and a principal stress elastic parameter characterization formula; (4) establishing a compressibility index characterization formula, and verifying and calculating a compressibility index comprehensive data body; and (5) quantitatively characterizing and predicting the formation compressibility. According to the method, effective characterization factors of shale formation compressibility are selected through multi-parameter analysis to establish a shale compressibility index characterization formula, so that quantitatively characterization of shale compressibility is realized, the identification standard of shale compressibility is established, target optimization of formation fracturing reformation layers can be guided, the cost of shale exploration is reduced, and the success rate of shale exploration is effectively improved.