Objective: To evaluate the immunity and influencing factors of diphtheria among preschool children in Shenzhen,to provide reference for effective monitoring of diphtheria IgG antibody level in preschool children. Methods: Serum samples were collected from 296 preschool children aged 4-6 who were recruited in Shenzhen. The diphtheria antibody titer in serum was determined by enzyme linked immunosorbent assay, and the effect of different immumuzation schedule including types of vaccine and vaccination timing, on the geometric mean concentration (GMC) of diphtheria IgG antibody and antibody positive rate were analyzed. Results: The GMC of diphtheria IgG antibody was 0.71 IU/mL, and the positive conversion rate was 33.1%. There were significant differences in antibody GMC and antibody positive conversion rate of diphtheria in different age groups( F/χ 2=11.77, 27.45, P < 0.01 ). The GMC and antibody positive conversion rate showed significant differences by diphtheria antibodies, vaccine types and end dose vaccination intervals( F=49.53, 12.95，11.61, P <0.01). There were statistically significant differences in the positive conversion rate of diphtheria antibodies in children with different types of diphtheria antibodies, vaccine types of diphtheria antibodies, and diphtheria antibodies at the time interval of final vaccination (Fisher exact probability method, P <0.01). Conclusion The overall positive conversion rate of diphtheria antibody in preschool children in Shenzhen is high. Timely completion of full diphtheria vaccination can improve the antibody level and plays a better role in protecting preschool children.