In a blog network, there are special users who induce other users to actively utilize blog services. In this paper, these users whose contents exhibit large influence over other users are defined as Content Power Users (CPUs). Accurately determining who content power users are in a blog network is important in order to establish an effective business policy that stimulates usage of blog services. In this paper, we propose a new method of determining content power users. First, we measure the influence of each document owned by individual users. Since the influence of a document tends to be high with long exposure, we adjust the value of influence of a document based on exposure duration. Then, by adding up the values of influence of all the documents owned by each user, we calculate the influence of the corresponding user. We analyze the performance of our method, by applying the proposed method to an actual blog network and comparing its results to those of preexisting methods for determining power users. The experimental results demonstrate that our method is well suited for the dynamic nature of the blog network.