The invention relates to a method for determining a large power microwave part higher-order passive intermodulation level. According to the method, (1), carrier wave frequency f1 and f2 are given in advance, intermodulation frequency fp(|m|+|n|)=m*f1+n*f2 is a positive value, the m and the n are non-zero integers and are opposite in symbol, and |m|-|n|=1; (2), a three-order passive intermodulation level measurement value Pmea3(i) of N powers is given in advance, i=1...and N, a total power of two paths of inputted carrier wave signals during passive intermodulation measurement is Ps(i), the two paths of carrier wave powers are identical, and Pc(i) is an ith test single circuit carrier wave power; (3), when a formula described in the specifications is the smallest, a non-linear relationship coefficient between a corresponding passive intermodulation input logarithm and an output logarithm is acquired, the PIM3(i) is the carrier wave frequency f1 and f2, and the carrier waver powers are identical and are the intermodulation level of the Pc(i) at the frequency fp3; and (4), according to the coefficient acquired in the step (3), the (|m|+|n|)-order passive intermodulation level PIM(|m|+|n|)(i) is determined, the PIM(|m|+|n|)(i) is the carrier wave frequency f1 and f2, and the carrier wave powers are identical and are the intermodulation level of the Pc(i) at the frequency fp(|m|+|n|).