On the basis of literature review, the study constructs an influence factor model of users' willingness to pay for knowledge in online question and answer community. The model is verified with the data from questionnaires. The results show that social influence, task pressure, thirst for knowledge and curiosity, perceived playfulness and technical ease of use are potential factors which influence users’willingness to pay for answers. Among them, social influence has the greatest effect. However, the effects of self-efficacy and platform trust are not significant. In addition, Income and working years displays significant negative correlation with willingness to pay.