Background: Few studies investigated the associations between dietary patterns and overweight/obesity among Chinese preschool children. Thus, the study aims to explore dietary patterns and their associations with overweight/obesity among preschool children in the Dongcheng District of Beijing. Methods: With a stratified proportionate cluster sampling, the study included 3373 pairs of preschool children and their guardians. Children’s weight and height were measured by school nurses, and their food and beverage consumption frequencies were reported by guardians via a food frequency questionnaire. Children’s age, gender, physical activity time, and sedentary time, as well as their parents’ highest level of educational attainment, occupation, weight, and height were also collected. Dietary patterns were identified through exploratory factor analysis. Among these identified dietary patterns, the one with the largest factor score was defined as the predominant dietary pattern for each child. The associations between predominant dietary patterns and overweight/obesity were tested by two-level random-intercept logistic models with cluster-robust standard errors. Results: Four dietary patterns, i.e., a “Sugar-sweetened beverage (SSB) and snack” pattern, a “Chinese traditional” pattern, a “Health conscious” pattern, and a “Snack” pattern, were identified. Among the children, 21.02% (95% CI: 19.68 to 22.43%) were predominated by the “SSB and snack” pattern, 27.78% (95% CI: 26.29 to 29.32%) by the “Chinese traditional” pattern, 24.90% (95% CI: 23.47 to 26.39%) by the “Health conscious” pattern, and 26.30% (95% CI: 24.84 to 27.81%) by the “Snack” pattern. After controlling for potential confounders, the “SSB and snack” pattern characterized by fresh fruit/vegetable juice, flavored milk drinks, carbonated drinks, flavored fruit/vegetable drinks, tea drinks, plant-protein drinks, puffed foods, fried foods, and Western fast foods was associated with a higher risk of overweight/obesity (OR: 1.61, 95% CI:1.09 to 2.38), compared with the “Chinese traditional” pattern. Conclusions: The preference for dietary patterns with high energy density but low nutritional value was prevalent among preschool children in the Dongcheng District of Beijing. Comprehensive measures to simultaneously reduce consumption of SSBs and unhealthy snacks among preschool children should be taken urgently to address the childhood obesity problem in China, particularly in metropolises.