Workers' unsafe behavior is the primary cause of occupational accidents in the construction industry, and workers’ behavior could be improved through observation, assessment, disposal and improvement. Following the BBS Approach, this study according to Application (APP) for handheld devices designed by IOSH that enables construction-firm managers to observe workers' behavior onsite. The BBS-APP in the construction site would help to generalize the workers' patterns and the unsafe conditions from the different job procedures through the observation of workers' activities and accumulated large number of observation records. The observations and records undergo statistical analysis to provide reference information for supervisors to rectify unsafe worker behavior and develop safety management strategies to prevent potential work hazards in advance.