Objective: To analyze the effects of health literacy on overweight and obesity among primary school students and their parents in terms of salt, oil and sugar reduction (referred to as the "three reductions"), so as to provide a theoretical basis for the development of obesity control measures. Methods: From March to April 2024, a total of 1 022 fourthgrade primary school students and 913 parents were surveyed in 24 classes in six counties in Shandong Province using multistage cluster random sampling, and physical measurements of primary school students were conducted. Pearsons correlation analysis and ordered multivariate Logistic regression were used to investigate the associations between health literacy of primary school students and their parents with overweight and obesity among children. Results: The detection rates of overweight and obesity primary school students in Shandong Province were 14.87% and 24.66%, respectively, with significant sex difference in obesity rate (29.46% for boys and 19.76% for girls) (χ2=12.93, P<0.01). In addition to students reducing oil scores, parental reducing salt,reducing oil,reducing sugar, comprehensive health literacy scores and students reducing salt,reducing sugar and comprehensive health literacy scores showed a negative relationship with students overweight and obesity (r=-0.10, -0.08, -0.07, -0.10, -0.04, -0.07, -0.03, P<0.05). The overweight and obesity rates among primary school students with high parental reducing salt,reducing oil,reducing sugar and composite health literacy scores were lower (OR=0.69, 0.69, 0.71, 0.63, P<0.05); and the overweight and obesity rate among students with high parental and low parental and high and low parental health literacy scores were lower (OR=0.68, 0.57, P<0.05). Conclusion Improving health literacy regarding "three reductions" for parents and children, especially parents, can effectively reduce the risk of childhood overweight and obesity.