Considering the effect of installation error, bending deflection and torsional deformation on load distribution, as well as drive feature of the gears, an approach based on the load sharing of modified double helical gears with the pinion axial float was proposed in which the modified tooth surfaces were represented by a sum of two vector functions that determine the theoretical tooth surface and the deviations surface fitted by 3 B-spline based on tooth surface mesh data from the longitudinal curves, and a TCA model including axial displacement and LTCA model was built. Besides, axial move process showed that the left and right tooth surface bore the same torques, so the modification was thought as a helical gear modification, and only one side tooth was considered and the other side was the same. In addition, minimum load density was used to evaluate load sharing, and genetic algorithm was used to optimize the parameter of curve. The results show that the axial motion process is about the tooth gap mutual compensation process which makes both of the tooth load distribution same and uniform, in short, when considering modification and axial motion, the loads tend to be uniform totally.