Objective To observe the preventive effect of Bailongjieyu granule on mental stress of naval officers and soldiers on voyage mission.Methods A total of 209 naval officers and soldiers were enrolled and divided into Bailongjieyu granule group (n=103) and blank group (n=106) by random number table method.The officers and soldiers of the 2 groups were investigated with psychological stress self-evaluation test (PSET) and symptom checklist 90(SCL-90) in their 1^st week of voyage.Only the officers and soldiers in the Bailongjieyu granule group were given Bailongjieyu granule in their 3^rd week of voyage.PSET and SCL-90 were retested respectively in the 2 groups in the 4^th week of voyage,and intergroup analysis was conducted.Results The baseline data of the 2 groups were basically consistent,and there were no significant differences in factor scores of PSET or SCL-90 between the Bailongjieyu granule group and the blank group in the 1^st week of voyage (all P>0.05).The standard score of PSET in the blank group in the 4^th week of voyage was significantly higher than that in the 1^st week of voyage (P<0.05).There was no significant difference in the standard score of PSET in the Bailongjieyu granule group between the 1^st week and the 4^th week of voyage (P>0.05).The standard score of PSET in the Bailongjieyu granule group in the 4^th week of voyage was significantly lower than that in the blank group (P<0.05).The SCL-90 scores of somatization,obsessive-compulsive symptoms,interpersonal sensitivity,depression,anxiety,hostility,fear,paranoia,psychotic,and other factors in the blank group in the 4^th week of voyage were significantly higher than those in the 1^st week of voyage (all P<0.05).The SCL-90 scores of depression,fear,paranoia and psychotic factors in the Bailongjieyu granule group in the 4^th week of voyage were significantly lower than those in the blank group in the 4^th week of voyage (all P<0.05).Conclusion Bailongjieyu granule can prevent naval officers and soldiers who are in voyage missions from military stress response.