The LEGO model was used to simulate the actual assembly line assembly operation, and a repetitive assembly task experiment was designed, taking into account the differences in the skills of adjacent assembly personnel, and the behavior performance data of the personnel combination during the task was recorded. Simultaneously, the fNIRS near-infrared device was utilized to track changes in HBO2 concentration in the prefrontal lobe of the assembled brain, in order to investigate the impact of differences in adjacent assembly personnel’s combined skills on job performance. The results of the experimental analysis show that the assembly error rate and task completion time do not show a relationship of first increasing and then decreasing with the difference in the skills of the personnel combination; however, within a certain range, the brain load of the personnel combination will increase as the skill difference increases. When the skill gap is too wide, it will play a part in reducing mental stress. As a result, when designing personnel arrangements to reduce worker load and improve production efficiency, manufacturing businesses should take into account the differences in skills between neighboring operators.