Abstract： Objective:To investigate the incidence of upper respiratory tract infection and the contributing factors in the officers and sailors of "Mission Harmony 2018".Methods:The officers and sailors of the Mission were selected as objects. The stratified sampling was adopted to investigate the incidence of upper respiratory tract infection and related factors during the long oceangoing mission.Results:During the long oceangoing voyage, the incidence of upper respiratory tract infection in the officers and sailors increased compared with that before the voyage, and the difference was statistically significant ( P<0.05). The proportions of newly-occurred upper respiratory tract infections during the long oceangoing voyage, from high to low, were common cold (52.31%), tonsillitis (13.85%), laryngopharyngitis (13.08%), and rhinitis (9.23%). Regarding the frequency of occurrence and duration of upper respiratory tract infection, the differences between those in the Mission and those before the Mission were significantly different ( P<0.05). Insomnia, fatigue, seasickness, and other factors contributed to the aggravation of upper respiratory tract infection ( P<0.05). The incidences of upper respiratory tract infection in the middle and the final legs of the voyage were significantly higher than that in the beginning leg, especially the incidence in the middle leg was the highest, and the differences were statistically significant ( P<0.05). The officers and sailors worried more about the complications of upper respiratory tract infection during the Mission than they did in non-mission periods, and the difference was statistically significant ( P<0.05). Conclusion:During the long oceangoing voyage, the immune function of the officers and sailors can be undermined by multiple factors, leading to the increase of upper respiratory tract infection, the aggravation of clinical symptoms, and the prolongation of the disease course, which can affect normal work and cause non-combat attrition. Therefore, it is of great significance to take certain measures to prevent upper respiratory tract infection.