Cardiorespiratory fitness (CRF) and adiposity contribute to high blood pressure (HBP) in adults and children. However, their relative importance as risk factors is unknown. We examined the relationships between weight status, CRF and HBP among Chinese primary school children. A cross-sectional study was conducted with 4926 school children aged 5-12 years. CRF was estimated from a modified Cooper test, body mass index z-scores and weight categories were calculated from objective height and weight measurements and BP was measured using an electronic sphygmomanometer. HBP was defined as >95th percentile based on reference cutoffs for Chinese boys and girls. Generalised Linear Mixed models, adjusting for age, pubertal status and height, were developed for boys and girls to explore the independent and combined associations between fitness, weight status and HBP. Seven hundred and fifty-two (15.3%) children had HBP, with a higher prevalence in obese (40.5% and 45.9% in boys and girls, respectively) and overweight (27.6% and 30.2% in boys and girls, respectively) compared with non-overweight (9.0% and 13.8% in boys and girls, respectively) children. HBP prevalence was lower in boys with higher CRF (odds ratio (OR) for the highest vs lowest CRF quartile in boys 0.64; 95% confidence interval (CI) 0.46-0.89). This association was not seen in girls. With weight status and CRF in the same model, weight status, but not CRF, remained significantly associated with HBP (obesity in boys: OR 4.19; 95% CI 2.63-6.67; in girls: OR 2.49; 95% CI 1.19-5.19). The interaction effect for CRF and weight status was non-significant. Overweight/obesity was significantly associated with HBP among children. There was no evidence of modification of this relationship by CRF.