群速度色散和高阶非线性效应是影响超强超短脉冲抽运下光参变放大能量转换效率的重要因素。为了提高光参变放大的能量转换效率，采用理论分析和数值计算的方法，模拟超强超短激光脉冲抽运下MgO∶LiNbO₃晶体中的光参变放大过程，得到了不同抽运功率密度、不同群速度色散条件下光参变放大的能量转换效率曲线，并且讨论了高阶非线性效应对和脉冲时间波形和频谱的影响。结果表明，群速度色散会使抽运光脉宽增加，功率密度降低；大功率密度抽运下高阶非线性效应的影响不可忽略，它会进一步减小能量转换效率，还会使信号光的频谱展宽，为了提高单位晶体长度的参变放大增益，可以通过引入初始啁啾来抵消群速度色散的影响。

Group velocity dispersion(GVD)and cubic nonlinearity effect can seriously affect the conversion efficiency of optical parametric amplification(OPA)pumped by ultra-short high intensity laser beams. Theoretical analysis and numerical calculation were used in order to increase the conversion efficiency of OPA in MgO∶ LiNbO₃ crystal. Some numerical results with different pump intensity and GVD conditions were reported and the variation of pulse time shape and spectral were explained by cubic nonlinearity effect. It is found that pump pulse intensity is seriously decreased and pulse width is increased by GVD. Cubic nonlinearity can't be ignored when pump intensity is high,which reduces the conversion efficiency and makes saturated crystal length longer. Initial chirps of pump pulse are introduced to compensate GVD and increase the gain of parametric amplification.