The numerical calculation of the shear lag effect of the thin-walled straight box girder and the thin-walled curved box girder is carried out respectively by using the finite element method based on the board shell unit-Shell 63 unit. The computational results agree well with the predicted value of variational method and the experimental data, which validates the exactness of the numerical method. Then primary research is carried out on computing the amount of deflection, stress, strain and shear lag coefficient of the thin-walled curved box girder under static load and analyzing the influence of curvature radius on the shear lag effect of the thin-walled curved box girder. The computational results show that curvature radius have significant influence on the shear lag effect of the thin-walled curved box girder, the shear lag coefficient increases as the curvature radius decreasing on the same position compared with the thin-walled straight box girder, and the amplitude increases more than 5%. Therefore, the curvature radius should be considered in the design of thin-walled curved box girders.