Objective:To analyze the causes of seasickness in the mission participants of the hospital ship Peace Ark during along oceangoing voyage, so as to provide a reference basis for optimizing mission participants drafting and reducing the incidence of seasickness in future.Methods:We recruited 260 volunteers from the mission participants of the hospital ship Peace Ark, and carried out a survey with a self-made questionnaire. The questionnaire includes two parts: Part 1 collected the demographic information, e. g. sex, age, body mass, and smoking history, and Part 2 was for analyzing the factors that might affect the occurrence of seasickness, e. g. the history of participating oceangoing missions, the current onboard job, the location of living cabin, the history of daily physical exercise before the mission, the history of daily physical exercise during the current mission, etc. A total of 251 responses were collected. All the data were analyzed by SPSS19.0 software.Results:Univariate analysis showed that there were significant correlations between seasickness and sex, weight, smoking, the history of participating oceangoing missions, the location of living cabin, and the current onboard job ( P<0.05). The results of multivariate regression analysis showed that the sex of female and the history of participating any oceangoing missions were the risk factors of seasickness ( P<0.05). The analysis of threshold saturation effect showed that from the second stage of the voyage on, the incidence of seasickness decreased by 0.51% after each stage. Conclusion:When drafting participants for oceangoing missions, the basic conditions of participants should be comprehensively evaluated. Those who were easily suffering from seasickness should be allocated to the living cabins as much at the middle or lower part of the ship as possible. The mission participants should pay attention to physical exercise, well-balanced nutritional intake, and the adaptive training of anti-seasickness.