Under the background of the rapid rise of new employment forms, whether employees taking side-hustle will have an adverse impact on their full-time job is a common concern in practice and academia. Through the questionnaire survey of 283 employees with side-hustles, this study constructs a dual-mediation model of the effect of employees’ side-hustles intrinsic motivation on full-time work performance based on the identity process theory, and discusses the moderation role of employees’ regulatory focus. The results show that identity conflict and identity enhancement play an mediation role in employees’ side-hustles intrinsic motivation and full-time work performance, and the promotion focus can improve the positive effect of employees’ side-hustles intrinsic motivation on full-time work performance, while the prevention focus can strengthen the negative effect between them. The above findings are helpful to fully reveal the effect of the side-hustles intrinsic motivation on the full-time work performance and provide useful reference for organizational management practice.