Background  Primary dysmenorrhea has a significant impact on women's physical and mental health, and there is a lack of epidemiological investigations of primary dysmenorrhea on a large scale and a large sample of young women who have been in the army for more than one year under daily training intensity.

  Objective  To investigate the incidence of primary dysmenorrhea in female soldiers at the grassroots level in northern China and its related risk factors, so as to provide evidences for the physical health guidance of grassroots young women.

  Methods  A self-made questionnaire and a mobile phone APP was used, the survey participants were selected by a cluster sampling of young women at the division (brigade) level or below in 7 northern provinces and cities from December 2019 to October 2020. The survey was conducted online and it included the basic situation, the menstruation situation, job training, living conditions, mental and emotional conditions and other items. After the subjects completing the questionnaire, the data would be uploaded automatically to the APP and the APP had the functions of data monitoring, locking and importing data into the database.

  Results  A total of 807 people participated in the survey, and 743 valid questionnaires were received, with an effective rate of 92.07%. The age distribution ranged from 19 to 35 (22.97 ± 2.38) years. Menstrual conditions were normal in 553 cases (74.43%) and irregular in 190 cases (25.57%). Of the 743 cases, 652 cases (87.75%) had normal menstrual period, while 91 cases (12.25%) had abnormal menstrual period; 469 cases (63.12%) had dark menstrual color or blood clots, 594 patients were affected with dysmenorrhea (79.94%), mostly were mild (76.00%); 252 patients were found to have dysmenorrhea accompanied symptoms (33.9%), and the common symptoms were fatigue (33.8%), low back pain (33.2%), irritability (27.8%) and diarrhea (17%). Univariate analysis of primary dysmenorrhea exposure factors showed that the probability of dysmenorrhea was associated with poor sleep quality, spicy food, frequent cold food or drink and high stress (P＜0.05). Logistic regression analysis showed that sleep quality, spicy eating, cold eating and drinking, younger age of menarche are the influencing factors of primary dysmenorrhea (P＜0.05).

  Conclusion  The incidence of dysmenorrhea is high among young women in the grass-roots army. Sleep and diet have obvious effects on the occurrence of dysmenorrhea. It is necessary to provide medical guidance and medical security to reduce the possible effects of bad living habits in young women in grassroots army.