In this paper

we point out that the conventional orthogonal condition of complex signals

which is stated in most references

is not a necessary condition of the orthogonality of the complex envelopes of bandpass signals in communication systems.Based on the equivalent lowpass method

the author derives the equivalent orthogonal condition of the complex envelopes of two real bandpass signals using the complex crosscorrelation function of the complex envelopes of real bandpass signals. It can be widely used for the orthogonality analysis of real bandpass signals in communication systems. The analysis of OQAM signal orthogonality is completely emphasized in both sides of same subchannel and adjacent subchannels.