Background: Cardiorespiratory fitness involves both cardiovascular and respiratory capacities. However, existing methods have been criticised for reflecting cardiovascular fitness, but not pulmonary fitness. The objective of this study was to investigate the relationship between these two testing parameters. Methods: A cross-sectional population-based physical fitness assessment was conducted in 23 schools. The body height and weight, lung capacity, and step test results of students aged 10-18 were recorded. Criterion-referenced standards from the China Sports Bureau were adopted, as they include separate measurements for cardiovascular and pulmonary fitness. Results: The Pearson coefficients of lung capacity and the step test index from 13,028 schoolchildren ranged from 0.007 to 0.086 and from 0.026 to 0.105 for boys and girls, respectively, showing that poor correlations exist between the two parameters. Cluster analysis resulted in three clusters of children with similar characteristics. A good degree of similarity was found between the two parameters in children obtaining an “excellent” grade, but only a moderate degree of similarity between the two parameters in those obtaining a “good”, “pass” or “fail” grade. Conclusion: When cardiovascular fitness and pulmonary fitness are considered separately, there is a poor correlation between them, thus indicating further studies of cardiopulmonary fitness measurements is necessary.