Objective: To understand the relationship between daily exercise load and physical fitness of primary school students, so as to provide relevant theoretical basis for the development of on campus physical education plans and the improvement of procedural physical health management for elementary school students. Methods: A total of 223 students from 6 classes in a primary school in Beijing were selected by a stratified random cluster sampling method from May to June 2023. The daily exercise load of the students was monitored by Polar Verity Sense heart rate armband. The duration of moderate to vigorous physical activity (MVPA) and daily Training Impulse (TRIMP) value were calculated, and the related indexes of daily exercise load were analyzed. Chi square test and univariate Logistic regression analysis were used to analyze the correlation between daily exercise load and physical fitness assessment levels, and multi factor ordinal Logistic regression analysis was used to explore the influencing factors of physical fitness assessment levels. Results: The average time spent in MVPA was (21.65±17.48) min. The TRIMP value was (361.47±124.81). The time spent in MVPA of primary school students in outdoor class, zero point sports, recess and after class PE were ( 8.86 ±8.56, 9.41±10.47, 1.97±3.12, 2.46±2.57) min, respectively. TRIMP values were (68.89±20.84, 72.83±30.27, 51.68±18.23, 19.99±5.78) in outdoor class, zero point sports, recess and after class PE, respectively. The results of univariate analysis showed that there were statistically significant differences in physical fitness levels among students with different genders, grades, and BMI ( χ 2=7.13, 19.04, 32.98, P <0.05). The duration of daily MVPA, along with TRIMP value during outdoor class, zero point sports, recess, and after PE class were all statistically significant with physical fitness levels ( OR =1.07, 1.05, 1.02, 1.03, 1.11, P <0.05). The results of multi factor ordinal Logistic regression analysis showed that the primary school grade (lower grade: OR =9.24, middle grade: OR =7.81), BMI (abnormal: OR =0.21), duration of daily MVPA in school ( OR =1.06), and TRIMP value during outdoor class ( OR =1.05) were statistically significant with physical fitness levels ( P <0.05). Conclusions There is a positive correlation between physical fitness and different grades, BMI, daily exercise load, and outdoor exercise load. Increasing daily exercise load can improve students physical health. It is suggested to tailor the school sports program to suit primary school students, increase both the intensity and duration of school daily sports, and promote procedural physical health management for elementary school students.