Fixed wing canard aerodynamic forces during flight control process was used as an energy source for internal control mechanisms, based on this kind of situation, control system was power up in flight control process, so we needed to initialize roll attitude angle of the fixed wing canard in flight. In this paper, a new algorithm based on aerodynamic synthesis vector analysis for the roll attitude initialization was presented, when the fixed wing canards was rotate around the projectile axis at a constant speed and the projectile motion was stable, the motion around the mass center met the instantaneous torque balance, so the control vector direction of the fixed canard is approximately the same as the aerodynamic lift vector caused by the dynamic balance angle, based on the above principles, initial roll attitude of fixed wing canard could be calculated by overload vector information. the algorithm was verified by simulation, based on simulation results , the range of roll angle error was −10° to 10°, it met the control index requirement.