A study on geometry design of spiral bevel gears based on conjugate curves is put forward in this paper. According to the theory of conjugate curves, generation principle and mathematical model of spiral bevel gears are developed for a given spiral bevel curve. The meshing equation in the given contact position for conjugate curves is derived. Tubular meshing surfaces contacting along the orientation of designated contact angle are proposed to build up the circular-arc tooth profiles, which inherit all properties of conjugate curves. Numerical example is illustrated for this research including the computerized simulation of three dimensional models and analysis of meshing characteristics. Theoretical and numerical results demonstrate the feasibility and correctness of conjugate curves theory. Compared with general spiral bevel gears, this novel gear is different in the viewpoints of meshing and generation principles. And it is expected to have more excellent transmission performance which will be further studied in future.