In this paper the typical interference sources for wireless communication in medium voltage (MV) switchgear are first studied and summarized, and the gap breakdown is then chosen as the primary interference source for IEEE 802.11b communication. The immunity tests to the interference of gap breakdown and narrow-band signals are carried out. The results show that both SF6 and vacuum gap breakdown have remarkable impacts on IEEE 802.11b communication. It is found that when the strength of radio signal is strong enough, it will also cause 802.11b working abnormally. According to the test results, the reliability performance of 802.11b devices is assessed preliminary.