The invention relates to an inversion determination method for rainfall type landslide shear strength parameters, and belongs to the technical field of slope engineering stability evaluation. The method comprises the following steps that 1, the basic characteristic value of the cohesive force cj and the internal friction angle (shown in the specification) of the side slope rock-soil body is determined; 2, the basic characteristic value of the side slope rock-soil body is obtained, 2, monitoring a slope monitoring point cumulative displacement value Si and rainfall intensity Qi; Step 3, determining the side slope underground water level Hi under different rainfall conditions at the ti moment; Step 4, determining a slope stability coefficient Fij under the basic characteristic parameter condition of all the c,(shown in the specification); 5, determining a slope stability coefficient F0i displacement equivalent monitoring variable Lambda i; 6, determining the correlation degree Lambda 0ibetween the slope stability coefficient F0i and the displacement equivalent monitoring variable Lambda i; And 7, determining the cohesive force cj and the internal friction angle (shown in the specification) of the side slope according to the grey correlation degree. According to the method, the calculation result is accurate, and the overall shear strength of the side slope can be better reflected. and moreover, the operation steps are easy to implement, and the calculation cost is lower than that of other determination methods.