The correct analysis of power spectrum density is very critical when assessing the radio frequency compatibility among GPS, Galileo and BD. Among a number of papers on this research, some, however, ignore the fact that short-code would produce line spectrum, and some present derivation results with errors. The above problems, instead, are given close attention by this paper. The paper firstly analyzes the characteristics of power spectral densities of Global Navigation Satellite Systems (GNSS) baseband signals, taking into account the real properties of the signals, such as code length, data rate, code chipping rate and characteristics of spreading code. And then it presents the detail derivation process. To verify the correctness of its results, GPS C/A code signal is taken as an example. The simulation of this research produces three results that include the line spectrum, real PSD and the spectral separation coefficient of C/A code in different data symbol period. It is concluded that the derivation results prove to be correct, and the data symbol period should be regarded as an important parameter of short code when assessing the radio frequency compatibility.
