Abstract: To solve the problem that traditional detection techniques could only detect partial common interferences and attend by high computational complexity in tracking telemetry & command(TT&C) system using code division multiple access(CDMA),a new transform selective mode distinguish(TSMD) technique with low computational complexity is proposed in the paper.This algorithm uses the performance of compression gain(CG) to detect impulse interference,linear frequency modulation(Chirp) interference and narrowband interference(NBI).If the result of detection is NBI,then,the type of sinusoidal tones(multi tones or single tone),digital NBI,or Autoregressive(AR) process is detected according to the performance of different NBI’s mean and variance in mode distinguish.The feasibility of this method is proved through simulations.