针对非共轴三阶自相关法测试中对二倍频光束的要求，采用分步傅里叶变换方法对入射高斯光束，使用KDP晶体I类匹配的二倍频过程时间波形演变规律进行数值模拟，给出二倍频光束波形仍为高斯分布的入射基频光能量范围.不同二倍频效率下基频光与倍频光脉宽比值不同，所得的三阶自相关函数脉宽则不同，导致与脉冲形状有关的半高宽度换算因子不是固定值.分析结果对三阶自相关仪的参数设计和三阶自相关法测试中的误差分析有一定理论指导意义.

Based on the requirement of the clean narrower second harmonic probe pulse, the Slip Step Fourier method is used to analyze the frequency doubling process in the third-order noncollinear correlator.The evolution characteristics of temporal profile are simulated for the Gaussian pulses and type I phase-matched of KDP crystal.The range of fundamental incident laser energy can be acquired with the second harmonic pulse shape remaining the Gaussian distribution.The pulse width of the third-order autocorrelation differences with the different ratios of full width of half maximum of fundament to second harmonic pulse at the different conversion efficiency of frequency doubling.This leads to the variable convolution factor of pulse width concerned with the pulse shape.The analyzing results are of reference value for the parameter design and error evaluating of the third-order autocorrelator.