Basing on the theory of the meshing principle and the differential geometry, deduced the contact wire function for the new sine gears. In explanation of the gear parameters influencing to the contact wire function, imitated the contact function using the regular changes values of the amplitude value H and the helix angle β with MATLAB. From the imitation derived the evolution of the contact wire influencing by the amplitude value H and the helix angle β. The contact wire moved following with the enlarge amplitude value H to the forward direction of the high tooth and the forward direction of the width tooth; The contact wire also moved following with the enlarge helix angle β to the negative direction of the high tooth and the negative direction of the width tooth. Thereby, in order to select the appropriate gear parameters provided basis.