Based on the generating line principle of spiral bevel gear, this paper researches the conjugation meshing mechanism of line contact between the meshing surfaces, and proposes a new theory for designing the tooth profile of spiral bevel gear. A certain tooth surface design of spiral bevel gear with spherical involute is analyzed deeply as an example. Key parameters of spiral bevel gear tooth profile are calculated by using space geometry principle, which include helix angle, generating line radius, modules and so on. Then the 3D solid model of spiral bevel gear is built by using the modeling software of CATIA, and key parameters are measured from the model. The measured values are equal to calculated values. It can be indicated that the teeth profile designed in this paper can mesh correctly. And the tooth surface can be generated with more simple movement.