To investigate the load transfer mechanism of hybrid girder joint with cells and bearing plate, a theoretical model was established to calculate this hybrid structure, based on the method of continuous elastic interlayer. This model considered the slip effect between concrete and steel, and the local press effect of the bearing plate. By comparing the calculation results of this theoretical model and a finite element model, and analyzing its affecting factors, the following conclusions were obtained. The discrepancy of accumulated axial deformation between steel and concrete works as a main reason of the fact that the maximum shear force of its connectors occurs at the end of the hybrid joint, far away from the rear bearing-plate. And this maximum shear force will experience a trend of first increase, then decrease and finally approaching to an invariable value, if the length of joint grows. Increasing the stiffness of the connector will lead to the increase of its maximum value, but in a relatively lower level. Increasing the axial rigidity of concrete or decreasing the axial rigidity of steel will both lead to the decrease of connectors’ shear force.