This study assesses the prevalence of mental health problems and their association with social media exposure during the COVID-19 outbreak in Wuhan, China. A cross-sectional survey was conducted among 4,872 Chinese citizens aged 18 years and older from January 31 to February 2, 2020. The study used the Chinese versions of the WHO-Five Well-Being Index (WHO-5) and the Generalized Anxiety Disorder Scale (GAD-7) to measure depression and anxiety, respectively. Social media exposure (SME) was assessed by asking participants how often they were exposed to news and information about COVID-19 on social media platforms. The results showed that the prevalence of depression, anxiety, and the combination of depression and anxiety (CDA) was 48.3%, 22.6%, and 19.4%, respectively. Over 80% of participants reported frequent exposure to social media. After controlling for covariates, frequent SME was positively associated with higher odds of anxiety (OR = 1.72, 95%CI: 1.31–2.26) and CDA (OR = 1.91, 95%CI: 1.52–2.41) compared to less frequent SME. The study highlights the need for governments to pay more attention to mental health issues, particularly depression and anxiety, during public health emergencies, especially in the context of the "infodemic" caused by misinformation on social media.This study assesses the prevalence of mental health problems and their association with social media exposure during the COVID-19 outbreak in Wuhan, China. A cross-sectional survey was conducted among 4,872 Chinese citizens aged 18 years and older from January 31 to February 2, 2020. The study used the Chinese versions of the WHO-Five Well-Being Index (WHO-5) and the Generalized Anxiety Disorder Scale (GAD-7) to measure depression and anxiety, respectively. Social media exposure (SME) was assessed by asking participants how often they were exposed to news and information about COVID-19 on social media platforms. The results showed that the prevalence of depression, anxiety, and the combination of depression and anxiety (CDA) was 48.3%, 22.6%, and 19.4%, respectively. Over 80% of participants reported frequent exposure to social media. After controlling for covariates, frequent SME was positively associated with higher odds of anxiety (OR = 1.72, 95%CI: 1.31–2.26) and CDA (OR = 1.91, 95%CI: 1.52–2.41) compared to less frequent SME. The study highlights the need for governments to pay more attention to mental health issues, particularly depression and anxiety, during public health emergencies, especially in the context of the "infodemic" caused by misinformation on social media.