Women aged 18–49 years are women of childbearing age. Their nutrition knowledge (NK) is not only related to their physical health but also affects the diet quality of the entire family and the health status of the next generation. Studies that assess the NK level of women of childbearing age using representative data in China are lacking. This study aimed to evaluate the NK level of Chinese women aged 18–49 years and explore influencing factors at both the individual and provincial levels. Data were from the Chinese Nutrition and Health Knowledge Survey 2021. A total of 38,065 females aged 18–49 years were included in the analysis. A face-to-face validated standard questionnaire was used to collect NK from respondents. The full score of the questionnaire was 100. Respondents who scored higher than 75 were considered to have NK. The Rao-Scott chi-square test was used to compare the differences in the NK awareness rate between or among the subgroups. A multilevel logistic regression model was used to explore influencing factors at the individual and provincial levels. All analyses accounted for complex sample design including clustering, stratification, and sample weights. The mean score of NK among Chinese women aged 18–49 years was 65.1 ± 11.8, and the awareness rate was 20.9% (95% CI: 19.6−22.3%). Among the five dimensions, the awareness rate of food safety was the highest (74.0%, 95% CI: 72.8−75.3%), and the dietary recommendation was the lowest (16.4%, 95% CI: 15.3−17.5%). The two-level logistic regression model analysis revealed that at the individual level, age, education level, occupation, chronic disease status and residence were the main influencing factors of the NK level. At the provincial level, the region and the female illiteracy rate were associated with the NK level. Dependent children ratio, per capita income, and health expenditure were not significantly associated with the NK level. The model accounted for 58.8% of the variance in the NK level. The NK level of Chinese women aged 18–49 years was low. Knowledge of dietary recommendations was weakest. Both individual and provincial-level factors were associated with the NK level. There is an urgent need to strengthen nutrition education actions for enhancing the NK of reproductive-age women effectively to improve their dietary behaviors.