Abstract: This paper discribes the effect of co-channel interference on the ground TT&C station between satellite-ground links.The effect of interference on a Carrier-to-Tracking Loop (CTL) is analysed, and the critical value is determined under the tracking condition of CTL.The analysis of the effect of interference on a telemetry demodulation subsystem is emphasized. The interference has an effect on the Bit-Error-Rate (BER) by two ways. On the one hand, the reference phase jitter caused by a carrier recovery loop will have an indirect effect on BER. On the other hand, the interference introduced directly into a coherent detection device will directiy give raise to increase BER.The results of the effects can be expressed in terms of the loss of input Signal-to-Noise ratio E_b/N_0 at the same BER.