The invention relates to a composite shock absorber for a polycrystalline diamond compact bit, comprising a drilling tool body having a water inlet, an impact body having a water outlet and forming a shock absorption cavity, a disc spring group having an annular pressing sleeve, a cylindrical torsion bar spring which has an external thread and a spline, is connected to the drilling tool body through threads and extended into an impactor and connected thereto through the spline, and the annular pressing sleeve, wherein bit vibration impact force is transmitted therebetween through a torsion transmission joint, and a bearing group is arranged between the lower end surface of the annular pressing sleeve and an annular step of the impact body. The composite shock absorber can weaken damage of the slippage effect to polycrystalline diamond compact cutting teeth, absorb axial vibration from a drill stem and prolong the service life of the bit.