Objective: In this study, the occupational fatigue caused by long-time sitting-posture work was studied. Also, the physical and psychological factors which affect on human fatigue of workers suffering from monotonous sitting-position were analyzed. Methods: In 2021, a total of 30 subjects, including 15 males and 15 females, were selected to complete a 4-hour simulated sitting-position assembly task in the laboratory. The "Borg's RPE" was used to measure the subjects' subjective fatigue and feeling of monotony, the polyconductive physiological recorder was used to measure the subjects' EMG, and the wireless motion-capture evaluation system was used to measure the kinematics of the subjects. Results: When engaged in monotonous work tasks, there was a significant positive correlation between workers' monotony and subjective fatigue, with correlation coefficients ranging from 0.976 to 0.988 (P<0.050) . At the beginning of work, the subjective fatigue of the neck was more significant (P=0.046) . As working time increased, the back fatigue was significantly higher than that of the neck (P=0.029) . After 4 hours of work, the MPF value of the back erector spinae EMG decreased significantly (P=0.025) . The body posture data showed that the shoulder and neck indicators began to change significantly after about 2 hours of work (P(neck)=0.032, P(shoulder)=0.021) . The waist and hip indicators began to change significantly after about 4 hours of work (P(left hip)=0.031, P(right hip)=0.028) . The flexion angle of the neck first increased and then decreased; the flexion angle of the waist and hip continued to increase with the working time. Conclusion: It was found that the fatigue effect of monotonous sitting-posture work on the operator is mainly reflected in the lower back. The monotony of the work exacerbates the operator's subjective fatigue feeling. The operator should be given corresponding protection and set the work content reasonably. It is recommended to have appropriate activities or short breaks every 2 work-hour.