Abstract: From the year of 1972, we began to examine the stepped bi-circular arc gear profile with both centers of convex and concave circular arc profile biassed from the pitch line. This kind of gear tooth profile has load bearing capacities much greater than the corresponding involute tooth load and instantaneously introduced to industry. Type of FSPH-75 gear profile has successfully used in many factories for high speed and heavy load transmission with soft or hard gear tooth surface. The shortening gear tooth of both biassed and bi-circular arc tooth profile for medium and low speed heavy load transmission with hard gear tooth surface has also been examined and used the finite element method to calculate the stress intensity with the help of electronic computer. The anther has made some reformations of bi-circular arc gear tooth profile which are stated in this paper, such as biassed gear profile to greatly minimized the running-in time, to enlarge the value of hx to 1.05 ha and make tip relief to obtain the most smooth transmission and what out.