A new guidance algorithm with threat avoidance ability and target sighting restraint is proposed for traditional staged guidance method lack of threat avoidance ability. Firstly, mathematic model of guidance is established based on relative velocity vector, second, the path restraint model is established based on threat avoidance, and guidance terminal restraint for target sighting is given. Value function is established based on rapidity, economical control and guiding precise, optimal control model for attack guidance is constructed with nonlinear boundary restraint, state restraint and path restraint. Gauss Pseudo spectral Method (GPM) is adopted to transform the problem into nonlinear programming problem. Simulation result shows, this new guidance algorithm is effectively for threat avoidance and the missile launch requirement is well satisfied by air combat requirement.