The velocity of the balance point is one of the most important parameters of calculation dry tray pressure drop.The calculation accuracy of the balance point is the most important factor affecting the judgment of the process of the valve’s opening.In this article,we identified the presence of no more than four balance points existed in the valve opening process by analyzing the experimental data,the arbitrary velocity points in the valve opening process are called balance points also.At the same time we use second-order Taylor expansion to approximate the parameter CD2,and the approximate expression’s coefficients are fitted by experimental data,the correlation coefficient and residual are 0.99999 and 0.00036,respectively