Initial in-situ stress is a primary factor for the design and construction in rock engineering. According to the data of Tongsheng tunnel of Shiyan-Fangxian express highway, different groups of in-situ stress in the tunnel site were acquired by adjusting lateral pressure coefficient. The residuals of different lateral pressure coefficients in isotropic and anisotropic constitutive relations were calculated by constructing a residual function. Through comparing and analyzing the results, the optimal lateral pressure coefficient for the tunnel site was confirmed. Furthermore, the in-situ stress of metamorphic rock at test points was retrieved.The constitutive relation of rock mass at the tunnel site was determined through comparison with measured values. Finally the distribution of in-situ stress field of the tunnel was obtained. The research shows that the initial in-situ stress field is related to the buried depth and the topography of tunnel. The anisotropic constitutive relation is adaptive for Tongsheng tunnel and the error is about 10%.