The invention relates to an automobile suspension frame system structure, in particular to a transmission mechanism of a passenger car rear axle independent suspension frame. The transmission mechanism of the passenger car rear axle independent suspension frame is in a left and right symmetrical structure in the boundary of a main reducer shell body center line. The left side structure is two pairs of cross-shaped shaft type universal joints. The two pairs of cross-shaped shaft type universal joints are composed of a transmission shaft, a left inner half shaft fork assembly and an outer half shaft fork assembly. The left inner half shaft fork assembly is connected with a sphere bearing assembly in an interference fit mode. The left inner half shaft fork assembly is fixed on the main reducer shell body. The outer half shaft fork assembly is connected with a lining assembly in a gap coordination mode. The outer half shaft fork assembly is connected with a left wheel side support frame assembly of one side through the lining assembly. The transmission mechanism of the passenger car rear axle independent suspension frame is simple in structure and high in bearing ability. The fact that the cross-shaped universal joint not only with the axial direction displacement delivering movement or with the angle displacement delivering movement are arranged on a driving shaft and a driven shaft can be satisfied.