Abstract: This paper researches the forced vibration in gearing of the geared systems by the principle of dynamics. As the mechanical models applied in this paper are jest like the practical structure of the geared systems, we can analyze the connection of the structural parameters to the forced vibration in gearing, completely. Properly optimizing all these parameters, the best match of the mass and rigidity for the gearing stability can be obtained. This paper presents a more accurate algorithm for the computer aided design.