How to increase users’ support for charity projects through appropriate gamification mechanisms on Online Fundraising Platforms for Charity (OFPC) has recently harvested significant attention in practice but not yet been systematically studied. Hence, this study examines the impact of gamification competition mechanisms on users’ intention to donate and repost on OFPC. Through an empirical experiment, we verified the impact of goal gradient effect by exploring how different gamification competition mechanisms on these platforms drive users’ motivation under different goal progress levels, thus affecting their intention to donate and repost. The results show that when goal-progress is high, cooperative competition mechanisms work better in increasing users’ perceived reputation, perceived social identity, perceived warm glow, and perceived altruism, which in turn improves users’ intention to repost and donate for charity projects.