A coherent ladar system for detecting vibration of a moving target was demonstrated. Micro-Doppler information was obtained to identify moving targets. Single frequency laser at 1.064 μm was input to a 4 km long single mode fiber to simulate the translation of long distance. A loudspeaker was used as the target with micro-motion. Back-scattered light from the target was collected by the receiving optics and coupled into a single mode fiber. A 3 dB fiber coupler was used to combine the received signal and the master oscillation, the output of the coupler was detected by a photodiode detector with 3.5 GHz bandwidth. The electrical signals of detector’s output were sampled by a high speed A/D card. The information of micro-motion can be extracted through the arithmetic of time-frequency analysis. With the delay of 4 km fiber, the lowest speed that the system can detect was 0.5 mm/s, the resolution of speed detection was in the order of mm/s, the resolution of frequency was in the order of kHz. Utilizing the technology of micro Doppler detection, the targets of different motion dynamics can be classified and identified.