A new method of combined quaternion and Euler angle was proposed to solve the singularity problem of Euler angle velocity equation at large extent attitude movement and all-attitude angles and jumping problems for the limitary of attitude angle using quaternion method in ejection seat performance simulation. Quaternion definition and geometry meaning were described and quaternion movement equation was introduced. Calculation formula of quaternion integral initial values in simulation was put forward through quaternion to Euler angle conversion. The problem of attitude angle jumping and discontinuous in simulation was analyzed. Simulation based on certain seat model was executed. Compared simulation result with experiment data and compared the result with another simulation using single quaternion method, it was shown that this method combined the virtue of quaternion and Euler angle velocity equation could efficiently resolve the singularity of Euler angle velocity equation and could realize all-attitude angle in simulation.