This study aims to introduce rational beliefs as a potentially relevant personal resource in the job demands–resources (JD-R) model to understand the underlying mechanism to reduce the job demand of work–home interface on self-rated job performance. Extending the JD-R model, this study explores the interaction effect of work–home interface and rational beliefs on self-rated job performance through the motivation process. A sample of 257 Chinese employees (58.4% females) filled in the questionnaire twice at a 6-week interval. Results of the moderated mediation model show that Time 1 (T1) rational beliefs moderated the mediating effect of Time 2 (T2) work engagement in the relationship between T1 work–home interface and T2 self-rated job performance. Specifically, when T1 rational beliefs were low, T1 work–home interface negatively predicted T2 self-rated job performance through lower T2 work engagement; when T1 rational beliefs were high, the conditional indirect effect was nonsignificant. Thus, intervention targeted to improve rational beliefs might benefit employees’ performance in organizational settings.