The intergroup bias in third-party fairness maintenance includes two components: ingroup love and outgroup hate. Previous studies revealed that intergroup bias could be alleviated by high social identity complexity. This study explored the influence of the social identity complexity of parties in unfair events on intergroup bias in third-party fairness maintenance. Participants were divided into two groups and asked to choose from retention and punishment (Experiment One)/compensation (Experiment Two) to respond to unfair events presented by dictator games. To separate the components, we introduced additional unaffiliated members. Social identity complexity included single identity, presented as ingroup vs. outgroup sides of unfair events, and multiple identities, which included group identity and five additional identities. The results demonstrated that third parties tended to impose less punishment and more compensation on outgroup members under multiple than single identity conditions; however, the punishment and compensation to ingroup members exhibited no significant difference between the identity conditions. These results indicated that the multiple identities of the two sides in unfair events can reduce intergroup bias in third-party fairness maintenance, which can be achieved by reducing the outgroup hate rather than ingroup love.