Under the backdrop of social commerce deeply penetrating consumer scenarios, multi-task online social referral programs have become a widely adopted marketing strategy by major platforms. However, the complexity of referral reward program mechanisms may exert varying degrees of influence on users’ referral intentions. Based on cognitive load theory, goal-setting theory, and equity theory, this study explores the impact of reward program complexity on users’ referral intentions in multi-task online social referral campaigns and validates the mediating roles of perceived decision rationality and perceived fairness through experimental methods. The results indicate that reward mechanism complexity has a significant negative impact on users’ referral intentions, with perceived rationality and perceived fairness playing crucial mediating roles. This findings expand the research perspective on incentive mechanisms for online social referrals and provides practical guidance for e-commerce platforms to optimize referral reward program designs and enhance user participation.