采用快速傅里叶变换（FFT）算法和Rung-Kutta法对KDP晶体中超短激光脉冲二倍频过程作了研究。详细讨论了群速度失配、群速度色散和三阶非线性相位调制效应对倍频光脉冲波形、光谱及转换效率的影响。研究结果表明：在超短激光脉冲二倍频中，三阶非线性相位调制效应可使二倍频光脉冲形状发生畸变，光谱明显展宽且转换效率降低；当入射基频光功率密度大于100GW/cm2时，三阶非线性效应是影响倍频过程的主要因素。

FFT algorithm and Rung Kutta method were adopted to investigate the frequency doubling process of the ultrashort laser pulse in KDP crystal. The effects of group velocity mismatch and dispersion, third-order nonlinear phase modulation on pulse shape, spectrum distribution and conversion efficiency of second-harmonic pulse were discussed. The results indicate that the modulation effect of the third-order nonlinear phase may distort the pulse shape of the frequency doubling, broaden the second-harmonic spectrum obviously and reduce the conversion efficiency. The third-order nonlinear phase modulation becomes the dominant factor to influence the process of the frequency doubling when the fundamental intensity of incident luminous power is over 100GW/cm2.