In view of the shear lag phenomenon in the measured data of continuous rigid frame bridge cantilever construction process, in order to solve the problem that the spatial bar element model commonly used in construction monitoring can not effectively reflect and calculate the shear lag effect on the box girder section in the actual construction process. The construction conditions of continuous rigid frame bridge in cantilever construction stage are simplified, and the simplified calculation models corresponding to each simplified construction condition are given. The calculation formulas of shear lag coefficient of each simplified calculation model are derived, and the cross-section stress of box girder in construction process is calculated by the calculation formulas and compared with the measured value. The comparison results show that the error of the stress value of box girder section calculated by the simplified calculation model is smaller than the actual value, which has a certain application value in practical engineering.