The micro-vibration activities of the biologic, including heartbeat and respiration, can be detected to identify the life targets, which is widely used in rescue, remote medicine, etc. A new life detection algorithm will be proposed for stepped-frequency continuous wave (SFCW) radar, which mainly based on multi-periods and MTD filter technology to extract the micro-doppler frequency of biologic targets. This algorithm also can get rid of the static objects and estimate the range of the biologic targets. We validate the algorithm by simulation and experimental results.