A numerical simulation and parameter optimization method for volumetric fracturing of an unconventional dual medium reservoir includes the following steps: based on the theory of dual-medium pore elasticity, in consideration of the friction effect between fractures, developing a viscoelastic-plastic damage model of hydraulic fractures based on explicit time integral; simulating random intersection and bifurcation of hydraulic fractures encountering with natural fractures by adopting a method of embedding zero-thickness fracture units in the inner boundaries of computational model grids, and establishing a mathematical model of hydraulic fracture expansion of volumetric fracturing in the unconventional dual-medium reservoir; compiling a finite element program for complex multi-fracture fracturing and competitive expansion during volumetric fracturing of the unconventional reservoir, and establishing a hydraulic fracturing finite element model of a casing-cement ring-perforation hole in cluster-reservoir matrix containing natural fractures.