Objective: To evaluate the intervention effect of school based salt reduction health education, so as to provide a scientific basis for constructing a more effective and sustainable salt reduction intervention model for children. Methods: According to a randomized controlled trial design, in June 2022, probability proportional to size sampling was used to select 501 second grade students (248 in the control group and 253 in the intervention group) from 10 primary schools in Zhenjiang (intervention group) and 10 primary schools in Yangzhou (control group), Jiangsu Province. An one year school based salt reduction health education intervention was implemented. This included 20 online and 8 offline health education sessions, monitoring of salt consumption in the canteen, and the establishment of a salt reduction environment on campus. The control group received no additional salt reduction interventions. A questionnaire survey and 24 hour urinary sodium test were conducted before and after the intervention. The difference in differences method was used to evaluate the intervention effect. Results: After the intervention, the intervention group showed significant net intervention effects in knowledge aspects, including knowing that primary school students consume less salt than adults ( OR=3.55,95%CI =1.69-7.47), daily salt intake of primary school students ( OR=6.64,95%CI =3.71-11.87), long term high salt intake leading to hypertension ( OR=6.83,95%CI =3.93-11.91), low salt intake not causing hair graying ( OR= 1.66 ,95%CI =1.00-2.75), salt content in food labels ( OR=4.56,95%CI =2.63-7.91), and common high salt foods ( OR=3.39,95%CI =1.87-6.14) (all P <0.05). In terms of attitude, the net intervention effect for having a positive attitude toward using less salt in home cooking was significantly increased ( OR=1.88,95%CI =1.13-3.12, P <0.05). There were no statistically significant net intervention effects for salt reduction related behaviors (all P >0.05). There was no statistically significant difference in the changes of 24 hour urinary sodium between the intervention group and the control group before and after intervention ( P >0.05). Conclusions School based salt reduction health education effectively improves students salt reduction knowledge and attitudes but has a limited effect on behavior change. The home-school collaboration should be strengthened, and the dietary environment should be optimized simultaneously.