The characteristics of inbound jamming signal for the satellite navigation system, which is organized by GEO satellites, is introduced. The inbound jamming level data from March 2 to March 9, 2012 is analyzed in detail by using robust spectral analysis method. The results show that: inbound jamming signal level varies greatly with period, and main period is 2.67 days, 1.52 days, 1.07 days, 0.82 days and 0.50 days. Larger contribution is made in the period of 2.67 days and 1.52 days.