Online opinion leadersare active communicatorswho are able to set the agenda for online discussions, provide thoughts from different perspective, and possibly change the attitude and behavior of other online community members. Online opinion leaders often are experts in one or more fields, and are in the center of social network. Zhihu.com is an SNS question & answer sites, which encourages people to share knowledge, experience, and ideas. Different from the opinion leaders in Weibo and traditional community, in which social identity is the key factor, the voting system and following mechanism have created a number of grassroot opinion leaders in Zhihu.com. Taking Zhihu.com as an example, this paper intends to examine the social influence of key opinion leaders in online community, and to better understand opinion leaders and the ecology of online community.