Objective: To evaluate the role of tuberculin skin test prified protein derivative (PPD) in defining the screening scope of close contacts of tuberculosis cases in disposal of tuberculosis outbreak in schools. Methods: In a senior middle school in August 2019, 1 553 students of the grade two were tested by PPD because of a school tuberculosis outbreak. PPD results were compared to grade one students without any association with this tuberculosis epidemic, who were also tested by PPD when beginning school. Potential association between PPD distribution characteristics and tuberculosis case distribution were analyzed. Results: Twenty nine grade two students were diagnozed as tuberculosis infection, seven of which were PPD positive, and with the same MIRU-VNTR genotype. In grade one, 0.1 % (1/796) student showed strong PPD positive, 34.3% (273/796) student showed positive. For grade two students, significant higher rate of strong PPD positive [5.9% (45/757)], and PPD positive [52.0% (394/757)] were observed ( χ 2=45.71, 49.90, P <0.01). Proportion of strong PPD positive in the first floor of the teaching building ( 19.4 %), where tuberculosis cases clustered, was significantly higher than that in other floors ( χ 2=89.81, P <0.01); Number of strong PPD positive students increased with TB cases in each floor of the teaching building ( r =0.99, P <0.01). Proportion of strong PPD positive and PPD positive in floors of the dormitory, where TB cases lived, was significantly higher than in other floors ( χ 2=49.4, 64.9 , P <0.01). Number of strong PPD positive and PPD positive students increased with TB cases in each floor of the teaching building ( r =0.84, 0.56, P <0.01). Conclusion Strong PPD positive rate well reflects tuberculosis infection of close contacts, and is recommended for defining the scope of screening.