This paper theoretically analyzes the difference of the judgement of current methods to locate the main harmonic source, and proposes a new method to locate the main harmonic source based on the nonfundamental apparent power in the IEEE Std.1459-2010. At first, this paper analyzes the current method, such us the index of voltage, current and active power, finds out that their judgment basis is different, so we get different results using different methods, and the key problem is that we do not have a reference standard to locate the main harmonic source, and the index of harmonic power can not evaluate the harmonic responsibility entirely. Standing in the point of the apparent power, it is more accurate to locate the main harmonic source by calculating the capacity occupancy of the utility and the customers. At last, by using MATLAB/SIMLINK to prove that this method is feasible on the condition of multi har-monic sources.