How to support the group argument is quite an important study of HWME research. An approach of expert opinion acquisition based on cloud model and evidence theory is proposed, with respect to the characteristic of group argument. According to the semantic relations between comments, this method uses cloud model to find out the opinion implicated in the comment, and synthesizes the implicated opinions into expert opinion on the base of evidence theory. A numerical example indicates that this approach can acquire expert opinion dynamically from the argument information and show the tendency of expert opinion.