Adverse childhood experiences (ACEs) are prevalent, costly, and associated with poor health outcomes in adults. Little is known about ACE prevalence rates or strategies for measuring ACEs among young adults in Mainland China. The aims of this study were to (a) translate the ACE-International Questionnaire (ACE-IQ) into Simplified Chinese, (b) assess the psychometric strength of the Simplified Chinese version of the ACE-IQ (SC-ACE-IQ), and (c) compare SC-ACE-IQ scores calculated using binary and frequency scoring methods. The ACE-IQ was translated from English to Simplified Chinese and evaluated for content validity, criterion validity, and test–retest reliability. Chinese young adults (n = 566) aged 18–38 years who were health science students were recruited in Shanghai, China from May to August 2020. ACE exposures were compared using binary and frequency scoring methods, as proposed by the World Health Organization (WHO). The SC-ACE-IQ has good content validity (S-CVI = 0.89) and test–retest reliability (ICC = 0.88). SC-ACE-IQ scores were associated with depressive (binary: r = 0.26, frequency: r = 0.29; p < 0.001) and anxiety (binary: r = 0.22, frequency: r = 0.24; p < 0.001) symptoms. Higher proportion of participants reported exposure to at least one ACE and four or more ACEs when using the binary scoring method compared to the frequency scoring method. The SC-ACE-IQ is a valid and reliable ACE measure for Chinese health science students. Using frequency methods may underestimate exposure to ACEs among this population. Researchers should carefully select scoring methods for different study populations and purposes.