Objective: To understand the changing trends and related factors of knowledge, attitude and practice (KAP) regarding the three major infectious diseases (acquired immunodeficiency syndrome, tuberculosis, hepatitis B) among freshmen in Jiangsu from 2019 to 2022, so as to provide a reference basis for the health education of infectious diseases in schools. Methods: From 2019 to 2022, a total of 33 944 freshmen from 20 universities in Jiangsu Province were randomly selected for four consecutive years to investigate their KAP levels online through self designed questionnaires on three major infectious diseases. The multiple linear regression model was used to analyze the changing trends of students KAP levels of the three major infectious diseases, and to explore the influencing factors of KAP. Results: From 2019 to 2022, the knowledge scores(18.0±3.1,18.4±3.2,18.7±3.2,18.8±3.2), related to the three major infectious diseases showed an upward trend ( F=436.50, P <0.01), and the positive attitude reporting rates were 81.77%, 81.46%, 82.68% and 81.74%, respectively. The reporting rates of positive practice were 80.11%, 79.25%, 79.08 % and 79.04%, respectively. Multiple linear regression showed that school type, parental education level, mother s occupation, average income per person in family and living arrangements during high school all had an impact on the knowledge ( β = -1.510 -0.559), attitudes ( β =-0.043-0.065) and practice ( β =-0.028-0.027) of the three major infectious diseases ( P < 0.05 ). The family residence areas only affected the reporting rate of positive attitude scores ( β =0.002-0.065), and whether only children or not affected the reporting rate of positive practice scores ( β =0.009)( P <0.05). The knowledge score showed an upward trend ( β= 0.297, P <0.01), the positive attitude reporting rate showed no statistically significant change ( β=0.001, P =0.22), and the positive practice reporting rate showed a downward trend ( β=-0.005, P <0.01). Conclusions Freshman in Jiangsu Province from 2019 to 2022 have shown a separation in KAP scores regarding the three major infectious diseases. Targeted measures should be taken to improve their health practice level.