Removal of harmful factors is very important to prevent work-related musculoskeletal disorders (WMSDs). The purpose of this paper is to propose the effective method for reduction of the harmful factors and improved methods that prevents the workers from musculoskeletal risks in a prosthetics manufacturer and the same business field with similar manufacturing condition and process. A questionnaire were adopted to research the symptoms of workers' musculoskeletal disorders, and an ergonomic investigation methods such as quick exposure checklist (QEC), rapid upper limb assessment (RULA), lifting index equation (NLE), and ovako working-posture analysis system (OWAS) were performed to search out harmful factors of manufacturing place and working posture. Therefore, this paper proposes methods of ergonomic evaluation to reduce the harmful factors. The methodology proceeded in this paper could be helpful for evaluating of harmful factors in the prosthetics manufacturer and the same business field with similar working environments.