In the context of digital technologies, computational thinking (CT) is considered a key competence of primary school teachers. However, assessment tools to measure in-service teachers' CT competence are rare. The current study explains the design, development, and validation of a scale to determine the in-service teachers' mastery level of their Computational Thinking Competence (CTC) in the Chinese context. The validity and reliability of the scale have been studied by conducting exploratory factor analysis (EFA), confirmatory factor analysis (CFA) and calculating internal consistency coefficients. The sample of this study consisted of 631 in-service teachers from different Chinese primary schools (EFA N = 189; CFA N = 442). The 31-item scale mirrors five factors: cognitive knowledge of CT, practices and skills of CT, attitudes and perspectives of CT, CT teaching design, and CT teaching implementation. The discussion of the results looks at the future use of the CT scale in Chinese educational settings that mirror a specific national education policy, talent demand, and educational culture.