Objectives Whether the routine delivery of diabetes-related knowledge can change patients' attitudes and hence influence their self-management activities remains unknown in primary healthcare settings in China. Thus, this study aims to explore the complex transformation process between knowledge, attitude and practice (KAP) among patients with diabetes in a city in China. Design A cross-sectional study. Setting Yuhuan City, Zhejiang Province, China. Participants A total of 803 patients with diabetes were invited to attend a questionnaire survey and 782 patients with type 2 diabetes completed the survey. The average age of participants was 58.47 years old, 48.21% of whom only attended primary school or below. Primary and secondary outcome measures A questionnaire based on existing scales and expert consultation was applied to assess patients' socio-demographic information (SI), disease progression risk and diabetes-related KAP. A structural equation model was built to analyse the relationships between patients' characteristics and KAP. Results No significant association was found between patients' knowledge and attitude (β=0.01, p=0.43). Better knowledge and attitude were both found to be associated with better diet and physical activities (β=0.58, p<0.001; β=0.46, p=0.01). However, patients with a more positive attitude toward diabetic care showed worse foot care practice (β=-0.13, p=0.02), while better knowledge was associated with better foot care practice (β=0.29, p<0.001). In addition, patients with higher SI (β=0.88, p<0.001) and/or disease progression risk (β=0.42, p<0.001) tended to present higher levels of disease knowledge. Conclusions While successful KAP transformation has been achieved in practice for diet and physical activities, there is a need to improve foot care practice. Health education should also prioritise the prevention, detection and care of diabetic foot. Also, appropriate methods should be adopted to deliver health education to vulnerable patients, such as the elderly, those living in rural areas, those with minimal education, the unemployed and low-income patients.