In this article, we use game theory to analyze and model human behaviors in a social network to achieve better system design. Such analysis and modeling is very general and can be applied to many social networks. From the discussion in this article, we can see that different game models should be used for different social networks with different types of interdependency. When designing a system, not only the system efficiency but also the fairness among users should be taken into account. Moreover, since users are rational and thus naturally selfish, they tend to overclaim what they may need and will not truly report their private information if cheating can improve their payoffs. Therefore, one should consider users' selfish nature and develop cheat-proof strategies to guarantee satisfactory system performance.