The processing parameters for cutting the high-temperature alloy steel (the mark is GH3128) by Nd∶YAG laser are studied. Eighteen experiments are conducted by the orthogonal method. The factors which influence the quality of laser cutting, including oxygen pressure, defocusing distance, cutting speed, input current, pulse width, frequency and error, are studied. The slag thickness and the kerf width are observed after laser cutting, and the comprehensive assessment is worked out. The influence of processing parameters on the cutting quality is studied by the intuitive analysis method. The optimal parameters are obtained, and verification experiments are conducted based on these optimal parameters. Interaction effect and block-group difference among these factors are studied by the variance analysis method, and the influence of interaction effect and block-group difference on the cutting quality is studied. The results show that the orthogonal method can optimize the slag thickness and the comprehensive assessment, but cannot optimize the kerf width.