Objective To investigate the change of disease constitution at different stages of a long voyage on the sea in a frigate. Methods The participants included the crew members in a frigate of PLA navy force. The disease types of the crew members were recorded at different stages of a long voyage on the sea in the frigate, including the whole voyage, early stage of voyage, middle stage of voyage and the late stage of voyage. Then, the disease constitution ratios at different stages was calculated, compared and sorted. Results It was found that the disease constituent ratios during the whole course, from high to low, was: respiratory infection,acute gastroenteritis,lumbar muscle degeneration,insomnia,kinetosis,dermatitis,oral ulcer,conjunctivitis,trauma,disease of cardiovascular system,paronychia and urinary calculi. The ranking during the early stage, from high to low, was: kinetosis, respiratory infection,trauma,acute gastroenteritis,lumbar muscle degeneration,disease of cardiovascular system,insomnia and dermatitis; the ranking during the middle stage was respiratory infection,acute gastroenteritis,lumbar muscle degeneration,insomnia,dermatitis,oral ulcer,trauma,conjunctivitis, urinary calculi and paronychia; and that during the late stage was: respiratory infection,lumbar muscle degeneration,insomnia,dermatitis,oral ulcer,acute gastroenteritis,conjunctivitis,kinetosis,disease of cardiovascular system,trauma,urinary calculi and paronychia. Conclusion Both the disease type and the disease constitution of the crew members change during different stages of a long voyage on the sea in a frigate