Abstract: Objective To probe into the principle of dynamic change of the physical health and ailing status among the personnel during working on a reef in the Chinese South Sea,so as to provide basis for making rational medical health guarantee projects.Methods To design the unified forms.All the work such as inquirement,test and noting down were done by uniformly tr ained medical wor kers.The visual vague scale was used in index.Results As the time on the reef prolonged,the weight of the personnel increased gradually,and reached to the hig hest level at the eleventh week.The average increment was 0.82 kg(P<0.01).Stamina index,healthy index,appetite index,sleep index,sleep time,the total count of sex arousing people and the degree concerning about the health of oneself were all reduced gradually(P<0.01).The counts of ailing people and using medicine people were higher in 1~3 weeks.Later,the counts were reduced wavily and touched bottom in the 6th week and the 10th week respectively.The count of ailing people was reduced more obviously(P<0.01~0.001).The trend of disease variety among persons was that the propo rtion of respiratory system disease was reduced and alimentary system disease was increased gradually,the proportion of skin disease was higher at the 7th week and locomotor system disease was higher at the 8th week,the proportion of diarrhea was reduced and constipation was increased gradually.Conclusion Working on the reef for 3 months,the physical health status and the degree concerning abouthealth of self of the personnel was reduced gradually.The count of ailing people and using medicine people were reduced wavily.