Abstract： Objective:To analyze the sleep quality of graduate-stage medical students in a university during their sea training course（campus preparation phase and sea training phase）.Methods:The Pittsburgh Sleep Quality Indicator Scale was used to survey 493 graduate-stage medical students of a university about their sleep quality. The questionnaires for the campus preparation phase were distributed and collected by the investigators of each group in class meetings from 8 May，2019 to 10 May，2019 and the questionnaires for the sea training phase were distributed and collected by the investigators of each group on the day of the end of the sea training（20 May，2019）in the ship’s cabin.Results:The PSQI scores of the graduate-stage medical students during the campus preparation phase and the sea training phase were（6.59 ± 2.46）and（6.65 ± 3.10），respectively，and the detection rates of sleep problems were 28.82% and 34.15%，respectively，with no statistically significant difference（ χ2=2.821， P=0.093）. The scores of three sleep quality factors，e.g.，subjective sleep quality，sleep efficiency，and sleep disorder，during the campus preparation phase were lower than those during the sea training phase，whereas the score of sleep duration during the campus preparation phase was higher than that during the sea training phase，all with statistically significant differences（ P<0.001）. Conclusion:Sleep quality problems are common among graduate-stage medical students in sea training courses，and great attention should be paid to students’ sleep quality during sea training to ensure that sea training is carried out smoothly.