The petrochemical method proposed in this paper is a new method developed through long-term practice and continuous innovation on the basis of Sansi algorithm, a petrochemical method to calculate the actual mineral content of granitoids from the chemical composition of rocks, which was put forward by Rong Jiashu in the 1970s. It designs corresponding calculating method for quasi-aluminous granitoids, aluminum supersaturated granitoids and aluminum strongly supersaturated granitoids, and simultaneously considers alkali metasomatic granites (or alkali feldspar granites). It is applicable not only to fresh rocks but also to partly altered rocks. This method is combined with the actual minerals as much as possible in dealing with the induction and assemblage of petrochemical analysis data and aims to make the calculation result consistent with the actual minerals in the rocks. The calculation process puts forward the correction coefficient χ of feldspar, which may correct the content of potassium feldspar and plagioclase in the rocks and ensure that the calculated results are consistent with the actual situation. Two kinds of parameters and related diagrams are obtained through the calculating results, one representing the percent content of the main forming minerals, such as Q, Or, Pl, Bi, Ms and Hb, the other reflecting the chemical characteristics of rocks, such as Ot, An_Pl, K-Na, a, b and Mg. This method can not only calculate the content of the main rock-forming minerals but also reflect the petrochemical characteristics, evolution process and metallogenic specificity.