Abstract: To explore the relationship between biological characters and soybean yield, this paper focused on selecting optimal function relationship between biological characters and soybean yield from eight types of functions by goodness of fitness (R²), root mean square error (RMSE), sum of squares due to error (SSE). The experimental results showed that the function relationship between height and soybean yield was Fourier1, and R², RMSE, SSE was 0.9228, 6.836 and 93.45, respectively. On the other hand, the function relationship between index of leaf area and soybean yield was Poly4, and R², RMSE, SSE was 0.7362, 71.87 and 319.2, respectively. In addition, the soybean yield changed from high to low when the plant height was in the range of 46-50 cm, and the yield was low when the plant height was more than 51 cm; the relationship between index of leaf area and soybean yield presented the right of parabola and soybean yield first increased and then decreased with the increase of index of leaf area.