Abstract: The geometric nonlinearity of synchronous trapezoid tooth belt is taken as the point of departure.A nonlinearity finite element solution of the synchronous belt is provided on the basis of elastic linear finite element method to solve two-dimensional stress distribution problem.The level stress distribution for a tooth of the synchronous belt is researched with help of this method.Finally,for an example,a maximum stress point and stress distributions of a synchronous belt tooth have been found out and compared with its elastic linear solution.