The purpose of this study was to investigate the effectiveness of microcomputer simulation, and to compare the differences in skill mastery and in the need for a teacher's assistance among students using a microcomputer with a partner, using a microcomputer alone, and those who did not use a microcomputer simulator in learning CNC programming skills;A pretest-posttest control group design was used in this study. All of the students obtaining scores in pretest were taken out from the research to assure the homogeneity of the subjects;A total of ninety students was randomly selected from five classes in National Yunlin Institute of Technology in Taiwan. These students were further randomly assigned to three groups;A Chinese microcomputer package was used for the research. The experimental process was completed in three weeks. There were a total of eighteen hours of instruction;A multiple covariance analysis was used to analyze the data. Students' previous experiences in mathematics, mechanical drafting, and computer concepts were used as control variables;The findings of the study revealed that mathematics scores and mechanical drafting scores did not have a significant effect on the posttest scores. The results of further analysis showed that there is no significant difference in achievement among those three groups. However, the number of questions raised per student in each group during the programming practice period was significantly different. Group one students, those who used program simulation packages individually, had significantly more questions per student than those who used program simulation packages with a partner or those who did not use a microcomputer. It was also noticed that during the experimental period students in the groups of using computers were more motivated in learning programming skills. It was therefore concluded that computer simulation is as effective as the traditional method. The teacher in a CNC laboratory could spend less time on students when they are working on a microcomputer simulator in pairs. The teacher then could spend more time helping students who are running programs on a CNC machine tool.