A new method is given to determine the load distribution factor K-beta of involute gears. Compared with the old method, the new one gives up some improper assumptions such as linear load distribution along gear tooth width. While considering the effects of bearing deformations, gear manufacture and assembly errors, gear axial force and gear tooth run-in on K-beta, the paper calculates K-beta according to "Load-Deformation Coordination" of gear tooth. Practical examples show that this method is more accurate, more effective than old ones.