In recent years, the detection of life signal using terahertz radar systems raises more and more attention due to the superior Doppler characteristics of terahertz band. In this paper, a 0.33 THz radar system was built and experiments on life signal detection were presented. The phase ranging algorithm was adopted and life signal was obtained under different conditions. From the results, we can conclude that phase ranging algorithm is a feasible method of life signal detection and has a number of advantages in the further research.