Objective: To understand the characteristics of sports load intensity of junior middle school physical education, and its relation with students’ physical fitness, and to provide suggestions for scientific arrangement of sports load of physical education. Methods: A total of 88 students from three grades in a middle school in Guangzhou were randomly selected. Polar heart rate tester was used to monitor the students’ heart rates during class, and physical fitness test was conducted on the students to obtain their physical fitness scores. Descriptive analysis, correlation analysis and one-way analysis of variance were used to process the data. Results: From the static characteristics, in junior high school physical education class, the mean of the lowest heart rate was 86.94 times/min, the mean of the average heart rate was 142.55 times/min, the mean of the maximum heart rate was 192.66 times/min, the average heart rate of junior grade one students was significantly lower than that of junior two students and junior three students (F=3.64，P<0.05). There was no significant difference in average heart rate between boys and girls (F=0.83，P>0.05); In terms of dynamic characteristics, heart rates at 3 and 31 minutes were significantly lower than those at 10, 17 and 24 minutes (F=13.87，P<0.01),in each part of junior high school physical education class, there were significant differences between grades, specifically, the heart rate of junior students was significantly lower than that of senior students (F=9.85，P<0.01); In terms of the correlation between exercise intensity and physical fitness, there was a significant negative correlation between the lowest heart rate, average heart rate, maximum heart rate and physical fitness(r=-0.34，-0.32，-0.29，P<0.01). Conclusion The physical activity intensity of junior middle school students is moderate and the average heart rate is within the range stipulated by "Chinese healthy physical education curriculum model".