Taking Xiangrui Street Bridge in Xining as the engineering background, which is a single-arch through continuous beam-arch combination bridge,based on the assumption of equal suspender force and filmy force, the method of structural mechanics is used to deduce the expression of the load sharing ratio of arch, the bending moment ratio of arch-beam and the deformation ratio of arch-beam, reveal the mechanism of beam-arch collaboration bridge under uniform load. The quartic parabolic curve is used to fit the suspender force. The error analysis of the formula and the finite element calculation result are carried out to determine the suspender force correction coefficient, so as to reduce the error caused by the assumption of equal suspender force. In the similar way, the cosine curve is used to fit the suspender force. The error analysis of the suspender force formula and the filmy force formula calculation results are determined from the filmy force correction coefficient, so as to reduce the error caused by the assumption of filmy force. Through the suspender force correction coefficient and the filmy force correction coefficient, the correction coefficients of the beam deflection, arch deflection and the proportion of external load sharing by the suspender force are finally calculated to be 1.1, 1.2, and 0.9 respectively, in order to reduce the formula error.