Objective: To understand the trends in malnutrition among primary and middle school students of Han nationality in Hainan Province from 2005 to 2019, so as to provide a basis for improving nutrition intervention measures for children and adolescents. Methods: A sample of 32 949 Han nationality primary and middle school students aged 7-18 years old in Hainan Province were investigated in 2005, 2010, 2014 and 2019 based on national survey on student physical fitness and health. The Malnutrition Screening Standard of Schoolage Children and Adolescents was used to screen malnutrition. Statistical analysis was performed using the χ2 test and the χ2trend test. Results: In the four surveys conducted during 2005 to 2019, the prevalence of malnutrition among primary and middle school students were 22.12%, 18.80%, 15.89% and 9.56%, respectively, with an increase of -12.56% and an average annual increase of -5.82%. The decreasing trend of malnutrition by year was statistically significant (χ2trend=600.72, P<0.01), and the proportion of emaciation type was the highest (8.87%-20.15%). The detection rates of malnutrition among all students aged 7 to 18 showed a decreasing trend from 2005 to 2019 (χ2trend=56.44, 60.04, 61.48, 42.49, 51.81, 50.81, 72.86, 101.34, 86.38, 24.81, 17.72, 10.38, P<0.01). From 2005 to 2019, the detection rates of malnutrition in boys were higher than that of girls (in 4 surveys), and that in rural students from 2005 to 2014 of 3 surveys were higher than that in towns (χ2=92.07, 35.16, 25.29, 29.98; 64.35, 4.26, 6.32, P<0.05). Conclusions The malnutrition of Han nationality primary and middle school students aged 7-18 years in Hainan Province show a trend of improvement year by year from 2005 to 2019, despite the overall high detection rate. Wasting is the most common type of malnutrition. The epidemic of malnutrition varies by age, sex and areas. Further targeted measures should be taken to strengthen intervention in the diet of primary and middle school students, to improve the nutritional status of children and adolescents.