Online games are becoming more and more popular nowadays. Interacting with others in games has also become a channel for establishing or developing social relationships. In this article, the author conducted an online survey (N=165) to study the relationship between types of in-game relationships, social capital, and psychological well-being. In-game relationships mainly include two types: playing games with friends and playing games with strangers. The author used the framework of social capital, which includes bonding and bridging. Regarding psychological well-being, the author selected two indicators related to social aspects, namely loneliness and relatedness. The author constructs a structural equation model. The results show that playing with friends will enable bonding and bridging while playing with strangers will enable bridging. Second, two different social capitals can both increase players’ feelings of relatedness and reduce players’ feelings of loneliness. This shows that social relationships in online games have a certain impact on people's psychological well-being. This research also provides some information for game design and understanding of social relationships in games.