The eccentric-loaded coefficients of more than 6 000 concrete cast-in-place box girders were analyzed by the secondary development of FEM software based on solid FEM,according to the relevant code of road and bridge. The results showed that the coefficient of eccentricity increased with the increase of the width-span ratio if the number of lanes was the same. It was found that the appropriate coefficient of a simply supported box girder could be taken from 1.15 to 1.5 and a formula was thus obtained to calculate the coefficient accurately. For the continuous box girder, the coefficient of each span could be solved by the above-mentioned formula, and revised according to the revised factor, with the maximum value taken as the coefficient of the bridge. The revised factor for the continuous box girder could be taken from 1.05 to 1.1. A larger correction coefficient was appropriate to select once the width-span ratio value was large or the span was far from the end of the beam, while a smaller one should be chosen on the contrary. In conclusion, this paper presented a batch method for establishing the solid FEM box girder model as well as its calculation and analysis processes.The method would be helpful in the study of the mechanical properties of the box girder, thus achieving a detailed and efficient design of it.