This study explores the impact of irregular overtime work in the working environment and job types on mental health, with special attention to workplace fatigue that may result from failure to properly adjust to stress. This cross-sectional study was conducted in January 2023. It used a structured questionnaire to investigate the stress adjustment situation of employees in a factory and analyzed its relationship with workplace fatigue or quality of life. The 241 valid questionnaires included respondents from different job categories and age groups, with the majority being women (77.59%) and those under 50 years old (70.54%). In terms of work nature, semi-finished product processing workers showed higher fatigue, and there are significant differences in overtime hours and fatigue. The findings further highlight possible differences in workplace fatigue among different groups and that targeted workplace health promotion programs may be needed to address these varying needs. In addition, the research results also remind managers that they should pay more attention to employees of specific age groups and specific work types to reduce their fatigue and thereby improve the overall healthy atmosphere in the workplace.