Background Obesity has become a significant public health problem within China. By observing dietary patterns, an individual’s actual dietary habit of nutrients or foods in combination can be identified. We aimed to examine dietary patterns in relation to the risk of obesity (body mass index (BMI) ≥ 25 kg/m²) and weight change (average weight change per five years) within a Chinese cohort. Methods We analyzed the data from 6,677 adults aged 18–65 years in the China Health and Nutrition Survey 1997–2015. Westernized, traditional Chinese, and high-starch plant-based dietary patterns were identified by principal components analysis. We estimated relative risks (RRs) and least-squares means (LS-means) with 95% confidence intervals (CIs) using the Cox proportional hazards models and the generalized linear models, respectively. Results High adherence to the Westernized dietary pattern was associated with increased risks of obesity and weight gain. Comparing top with bottom quintiles, RR (95% CI) for obesity (BMI ≥ 25 kg/m²) was 1.57 (1.26–1.95; P for trend < 0.001). LS-means of weight change (kg/5 years) were 1.73 (0.98–2.47) and 1.13 (0.39–1.87; P for trend = 0.036) in the top and bottom quintiles, respectively. Increased weight gain among those following the Westernized dietary pattern was stronger in the Southern region than the Northern region. There was a slight hint of an inverse association between the traditional Chinese dietary pattern and obesity. We did not find any significant association for the high-starch plant-based dietary pattern. Conclusions The Westernized dietary pattern increased the risk of obesity among Chinese adults. Weight gain associated with Western dietary pattern was more pronounced in the Southern region than in the Northern region. Our study will provide helpful data in developing dietary guidelines for the prevention of obesity specific to different regions in China.