Objective To develop a trauma and stress exposure scale for peacekeepers and to evaluate its reliability and validity. Methods The theoretical and structural models of the scale were determined based on literature review and interview, and an item pool was established, which was revised by experts to form basic items. In Oct. 2019, 733 soldiers and officers from 2 peacekeeping infantry battalions to South Sudan were tested, items were screened through project analysis, and basic scale was formed by exploratory factor analysis. A confirmatory test was conducted on 595 officers and soldiers of another peacekeeping infantry battalion to South Sudan in Jan. 2020. The reliability of the scale was verified by the Cronbach’s α coefficient and the split-half reliability test scale, and the validity was verified by correlation analysis and confirmatory factor analysis. The post-traumatic stress disorder (PTSD) check list-military version (PCL-M) scale was used as the calibration table to test the calibration correlation validity, and the predictive validity of the scale was evaluated by ROC curve. Results The scale finally included 25 items in 5 factors (traumatic events during peacekeeping, personal life stressors, interpersonal stressors, task evaluation and past traumatic events), with an overall cumulative contribution rate of 62.909%. Confirmatory factor analysis showed that the Cronbach’s α coefficient was 0.909 for homogeneity reliability and 0.806 for the split-half reliability of the whole scale. In the structural validity test, all the fitting indexes were in the ideal standard range (χ²/df=2.438, root mean square residual=0.042, and root mean square error approximation=0.082). The score of each dimension was positively correlated with the total score (r=0.411-0.727, all P<0.01). The calibration correlation validity between the total scores of the scale and the PCL-M scale was 0.623 (P<0.01). The predictive validity of the scale was calculated at 5%, and the area under curve was 0.937 (95% confidence interval 0.907-0.967). Conclusion The trauma and stress exposure scale for peacekeepers has been preliminarily developed after strict item selection. The items of the scale are in line with the principles of good representativeness, high sensitivity and good differentiation, and meet the requirements of the development.