Objective: To analyze and compare the correlation between body mass index (BMI) and cardiopulmonary fitness of children and adolescents aged 7 to 18 years in China and Japan, and to provide important reference for healthy development promotion of children and adolescents in China. Methods: A total of 9 594 children and adolescents aged 7-18 years in China and Japan were selected and examined for height, weight and 20 meters shuttle run test (20mSRT), 4 800 of whom were randomly selected and included for analysis. Independent sample t test was used to compare the differences of BMI and 20mSRT between Chinese and Japanese children and adolescents of different sex and age. Logistic regression was used to compare the odds ratio of high cardiopulmonary fitness among children and adolescents of different nutritional status. Pearson correlation and linear regression were used to analyze the correlation between BMI and 20mSRT. Results: Odds ratios of high cardiopulmonary fitness were 0.57, 0.52 and 0.33 in wasting, overweight and obese children and adolescents in China, and 0.49, 0.36 and 0.16 in Japan, respectively, with significant differences(P<0.05). The BMI-Z scores of Chinese and Japanese children and adolescents ranged from - 2.72 to 8.76. There were significant differences in 20mSRT-z between different BMI-Z groups(P<0.05). The 20mSRT-z score of Chinese and Japanese children and adolescents initially increased with BMI-Z score and then decreased with the increase of BMI-z score. With the decrease of BMI-Z score, 20mSRT performance in Chinese boys decreased significantly. Conclusion Compared with the normal weight peers in China and Japan, the proportion of wasting, overweight and obese children and adolescents with high cardiopulmonary fitness is lower. The BMI-Z score and 20mSRT-z score shows a general inverted "U-shaped" trend. The effect of wasting on cardiopulmonary fitness is greater in Chinese boys.