Drawing upon positive behavior theory and resource-based theory, we construct a moderated mediation model. Taking organizational slack as a moderator and job crafting as a mediator, the model explores the relationship between positive personality, employee work performance and boundary conditions. Using 195 bank employees as the research objects, we test the direct and indirect effect of the model. The results of hierarchical linear model show that job crafting positively mediates the relationship between positive personality and employee work performance; organizational slack positively moderates the mediated relationship among the three variables, and it has a non linear, inverse U-shaped moderation on the relationship between positive personality and employee work performance.