Abstract: Rebuilding the trace of a free-fall body in the vacuum is one of the key steps in findinggravitational acceleration from the sampled fringe signals. This paper proposed an algorithm for rebuilding the trace during the independent process of developing small Laser Interference Absolute Gravimeter. The basic principles are: ① Computing the time of the points before and after zero-crossing of a completely sampled fringe signal, which is generated by a freely falling body, and getting the time coordinates of zero-crossing points; ② Dividing these time coordinates to get the Time-Displacement Coordinates in the body trace using the same displacement interval. In the experiment, we found that it needs 2.5 s to complete one calculation, the average timing accuracy is plusmn;0.01 ns, the induced error is 5.2times;10-12 m/s2, and one complete measurement time is 15 s. The results satisfy the demand of the measurement speed and the accuracy in developing the high precision laser interference absolute gravimeter.