Massive Multiplayer Online Games (MMOG) have attracted millions of players in recent years. In MMOG, players organize themselves voluntarily and fulfill collective tasks together. Because each player can join different activities, one player may show different social relationship with others in different activities. In the paper we proposed the incremental label propagation algorithm to search the cliques accurately and quickly. Then we analyzed community structure characteristics on multi-activities. It's shown that the existing guild organization cannot satisfy the requirements of multi-activities in MMOG, which motivates us to devise new community communication channels and platforms in future.