Drawing on the job demands-resources (JD-R) model and affective events theory (AET), the present study used the Job Resource Scale, Positive and Negative Affect Schedule, and State Job Performance Scale to examine the relationship between daily job resources and job performance, focusing on how emotions mediate this relationship from a within-person perspective. Fifty-eight full-time counselors from two universities in China were recruited by convenient sampling. We used an experience sampling method, collecting two surveys per day for 10 consecutive workdays ( N = 580 full day-level data points). The sample consisted of 63.8% women and 36.2% men, and their average age was 32.26 years ( SD = 3.49). Our multilevel path analysis results showed that: (1) day-level job resources are positively related to day-level job performance, day-level positive emotion, negatively related to day-level negative emotion; (2) day-level positive emotions are positively related to day-level job performance, while day-level negative emotions are not related to day-level job performance; (3) day-level positive emotions mediate the positive relationship between day-level job resources and job performance, whereas day-level negative emotions did not show a significant mediating effect. The current study provides a within-person perspective for testing the applicability of theoretical models and serves to inspire practitioners in the domain of university management.