Missiles will be flying under the condition of high angle of attack. To fit this condition, a new kind of 3-D non linear guidance law is needed. A time varying state space equation is built through the analyzing of the relative movement model between missile and target. With the analysis of the equation, the sliding control theory can be used to design the guidance law. Also the 3-D guidance law is designed under the condition that the pitching channel and yaw channel are strongly coupled. The simulation results show that the angles between missile and target can be fixed in a short time, this designed 3-D guidance law can fit the non linear flying condition.