Objective: To analyze the relationship between the baseline BMI level and body mass index (BMI) changes of primary and middle school students and the blood pressure level and the risk of elevated blood pressure after 8 years of follow up(also known as the end stage), so as to provide a basis for the prevention and control of blood pressure in children and adolescents. Methods: The physical examination data of 9 748 primary and secondary school students were selected from a cohort study design in Longkou City, Shandong Province for 8 years from 2014 to 2022, and analyzed the association of baseline BMI level and BMI changes with end stage blood pressure level and the risk of elevated blood pressure. Chi square test was used to compare differences between groups, and the generalized linear model and Logistic regression model were used to analyze the effect of baseline BMI level and BMI changes on blood pressure level and elevated blood pressure after 8 year follow up. Results: Among non overweight and obesity group at baseline, the prevalence of high blood pressure was 9.1%. Among the overweight and obesity group, the prevalence of high blood pressure was 12.0%. Under different BMI status at baseline, the incidence of high blood pressure in boys was higher than that in girls. Compared with the BMI Z value≤-1 group, with the increase of BMI Z value, the systolic blood pressure level and the risk of high blood pressure gradually increased; with the BMI change continuously low as the control, sustained high and increased groups showed an increased risk of end stage high blood pressure ( OR=4.00, 2.21, P <0.01), and boys had a greater risk of elevated blood pressure. Conclusion Children and adolescents with higher baseline BMI level and increased BMI changes are at a higher risk of elevated blood pressure. Therefore, secondary school students should monitor the occurrence and development of blood pressure level in real time, and take comprehensive and effective measures to control the occurrence of elevated blood pressure level in childhood.