Abstract: In the forestry production,the accidents,caused by the case of body unbalanced like tumbling and falling,have a tight relationship with equilibrium function. Therefore,study on equilibrium function is very important to ensure the safety of forestry production,and the BSR-1 Body Balance Testing Instrument was worked out on this purpose. In order to improve the testing precision of the envelope size of body barycenter swaying trajectory,one of the indices of the instrument,the recording mode and characteristics of the instrument were studied in this paper.An optimal algorithm to the instrument was put forward based on the study of several algorithms.The new software of the BSR-1 Body Balance Testing Instrument was compiled.It has been proved that the new software can calculate the envelope size of human body barycenter swaying trajectory accurately.