In this paper, the properties of time and frequency domain of pulsed CO 2 laser difference frequency signals with CdTe electrooptic modulator are studied in detail. The long pulse trailing is found in time domain, and the trailing time bear a relation to outer trigger voltage of CdTe crystal. If it is very weak, the pulse signals can hardly be received through direct detection. In this case, the strong difference frequency signals from pulse trailing will be received if heterodyne detection is used. According to the controllability to trailing time, the possibility of intermediate frequency signals trace and frequency-offset lock between short-pulse transmitter and CW local oscillator light in pulse laser heterodyne is discussed.