The invention relates to a fatigue solving method of a car frame under the effect of spatial rotation moments. The method comprises the following steps that: a finite element model of a car frame structure under a permanent load is built, and a static solving result under the permanent load is output according to the finite element model; a moment load is exerted on the car frame, and translational constraints in three directions (X, Y and Z) are exerted in positions of support legs; under the condition that the support counter force in the three directions (X, Y and Z) in the positions of the support legs does not generate a negative value, the static solving result of change loads only including the moment load is output, and the static solving result is loaded into a fatigue solving work condition; and then, according to the rotating sequence of the space moment load, the car frame material attribution, a material processing method and a fatigue solving method, the car frame is subjected to fatigue cycle solving, and the fatigue service life and the load cycle amplitude are output. The fatigue solving method has the beneficial effects that the permanent load and the spatial rotation moment load are processed in different steps, so the fatigue solving result of the car frame under the condition of coexistence of the spatial rotation moment and the permanent load is obtained.