Abstract Background The Trunk Impairment Scale (TIS) has been translated into Chinese, but the psychometric properties of the Chinese version of the TIS (TIS-C) have not yet been established. We aimed to examine the reliability and validity of the TIS-C for assessing sitting balance among Chinese people with a stroke. Methods A descriptive, cross-sectional design was used. We recruited a convenience sample of 170 subacute stroke patients aged 18 years or over from the neurology departments of four traditional Chinese medicine hospitals in China. Patients completed the TIS-C, the Berg Balance Scale and the Modified Barthel Index. The psychometric properties of the TIS-C were examined to establish test–retest reliability, internal consistency, equivalence, and content, criterion, and construct validity. Results Intraclass correlation coefficients for inter-rater and intra-rater reliability ranged from 0.75 to 0.89 and from 0.90 to 0.97, respectively. The TIS-C Cronbach α was 0.86. The strong correlation between the total score of the TIS-C and the Berg Balance Scale (r s = 0.81, p < 0.001) or Modified Barthel Index (r s = 0.84, p < 0.001) suggested good concurrent and convergent validity, respectively. Known-group validity was supported by the significant difference (p < 0.001) in TIS-C scores between participants with mild and moderate stroke. Conclusions The TIS-C is a valid and reliable tool for assessing static and dynamic sitting balance as well as coordination of trunk movement among stroke survivors with mild and moderate stroke.