This paper investigates the impacts that intermediaries may have on transaction efficiencies and market scales in electronic commerce. By comparing the utility levels of both buyers and sellers in two different market structures in our model, which refer to direct transactions between sellers and buyers, and transaction with intermediaries respectively, this paper point out the precondition under which intermediaries may exist. The impact of intermediaries on market scale is further explored by taking comparative static analysis on the influences of real transaction price change, and intermediaries' transaction efficiency on market scale. Finally, it is concluded that information asymmetry doesn' t necessarily lead to low market transaction efficiency and intermediaries are still needed in E-commerce if the benefits are larger than information costs.