Abstract: In order to meet the design requirements of low profile, the transceiver switch in T/R module generally adopts the design of single pole double throw (SPDT) switch with high integration. When the active voltage standing wave ratio increases with the increase of the scanning angle of the active phased array antenna, the impedance mismatch between T/R module and antenna radiation element will inevitably occur in active phased array antenna that applies SPDT switch in T/R modules. In this paper, the impedance mismatch problem is analyzed by impedance deflection experiment of T/R module, the transmitting output peak power, transmission efficiency and transmission channel phase of the module are quantitatively presented and discussed, showing the influence of T/ R module impedance mismatch on emission performance. The T/R modules are applied in an active phased array antenna, and its influence is further discussed by testing EIRP.