AimTo identify the intention of Chinese pregnant women to undertake physical activity (PA) using the theory of planned behaviour.DesignA cross‐sectional survey.MethodsFrom April – October 2017, a cross‐sectional questionnaire was completed by 746 pregnant women from the Health Birth Cohort in Wuhan, China. The theory of planned behaviour variables as well as sociodemographic characteristics was recorded, and the Pregnancy PA Questionnaire was together used to assess their PA during pregnancy.ResultsOnly 11.3% of the women met the international guideline. The intention to undertake PA was found it to be positive in 63.9% of pregnant women. Structural equation modelling analysis revealed that behavioural attitudes, subjective norms, and perceived behavioural control (PBC) influenced PA by directly influencing the behaviour intention. Both behavioural attitude and subjective norms influenced PA by indirectly affecting the behaviour. Overall, the model described 60% variance of the behavioural intention to undertake PA during pregnancy.ConclusionPBC was confirmed to be a prominent factor in determining behavioural intention to undertake PA during pregnancy. Pregnant women should be helped and appropriately guided by health providers to overcome barriers to PA.EffectThis study investigates the effect of perceived behavioural control (PBC) on the intention to undertake physical activity (PA). The findings suggest that nurses’ and midwives’ attention should be focused on how to promote the improvement of perceived behavioural control ability of pregnant women to improve pregnant women's PA intention. The attitude of pregnant women on taking up PA and their ability to control behaviours can be improved with support from family or healthcare providers.