Most navigation satellites transmit navigation signals within L band, such as GPS, Galileo, BeiDou and so on. Solar radio bursts frequently occurred also with strong emission in L band, which are potential interferences for the navigation service. During the most intense solar radio bursts, the obviously decreasing performances of navigation systems were found. In this work, we get the threshold values for the three communication frequency points by theoretical arithmetic. At the same time, we will set up the real-time solar radio flux monitor system for test and verify the real threshold value in natural space based on 10m solar radio telescope. At last, we will try to build the pre-alarm system combining optical observation data.