Background: Computational thinking (CT) has been broadly considered one of the 21st-century competencies, and an emerging trend has been seen in integrating CT into primary education. Cumulative research was conducted to investigate the influencing factors of CT learning performance, and an ample range of factors has been identified, involving both cognitive and non-cognitive facets. However, limited has been done in exploring the non-cognitive factors, and even less at the primary education level. Objective: To address this gap, this study bridged CT with personality in the primary school context, and more importantly, it proposed a mediator in the personality-CT relationship that is, attitudinal beliefs, which are amenable to change, thereby allowing further support for nurturing the traits. Method: Based on the Big Five model of personality, standard tests were administered to a sample of 434 primary school students (ages 8-11), and data were analysed using structural equation modelling via Mplus. To improve the robustness of the results, control variables (i.e., demographic features, coding experience) were added to the research model, and a bootstrap approach with 5000 resamples was used to examine the mediating effect. Result and Conclusion: Findings demonstrated that "Conscientiousness" had a positive effect on CT, and attitudinal beliefs mediated the effect of "Open-mindedness" (positive) and "Negative Emotionality" (negative) on CT. The study contributes to the literature by enriching the CT network with non-intellectual components and unravelling the mechanism of CT regarding how disposition traits turn into learning performance. The results implicate practitioners on the importance of encouraging conscientious behaviours and nurturing positive attitudinal beliefs in CT primary education.