Abstract: The compensated linear vector dipole （CLVD） source is usually induced by underground explosions and could lead to a null in the Rg spectra. There is a theoretical scale between the null frequency and the depth of the CLVD source. Therefore we can estimate the depth of underground explosions with the null frequency. However, this relationship is based on simply considering the CLVD source while the conjunct effects of ISO and CLVD sources are neglected. This study researches the conjunct effects of ISO and CLVD sources in underground explosions on the spectral null in Rg waves by numerical calculation of the Rg spectra with seismology theory of surface waves. The results indicate that the null in mixed signals is quite different from the results of single CLVD source. Thus the null frequency of Rg waves is not simply corresponding to the theoretical value in practical underground explosions and it is improper to estimate the depth of explosions by directly applying the theoretical formula.