The existing computational methods of displacement release coefficient are too complex. Based on quadratic regression orthogonal design，a construction method of displacement release coefficient formula was given，and a series of numerical experiments of a circular tunnel in hydrostatic stress field were carried out by the above method. The regression equation of displacement release coefficient was established，and the sensitivity of parameters was determined. Through analysis of numerical examples and a case history，the equation was proved to be reasonable and effective. The results indicate that for different levels of surrounding rock，the effect of the same factor on the displacement release coefficient of the tunnel face is different. Stress level，disturbance of rock mass，GSI，H-B material constant and Poisson's ratio have a great influence on the displacement release of tunnel face，while the intact rock strength and deformation modulus have little influence.