We present a method for preserving time-invariant phase relationships

through introduce a third signal as a reference

when ratios are taken between two complex signals that are harmonically related.We prove that the theory taking fundamental signal as a reference to be able to eliminate the phase ambiguity is effective.After that we provide a simple example to illustrate this conclusion and show how to apply this technique when calculating nonlinear large-signal scattering function.In the practical application this algorithm manifests to have a broad application prospect.