Abstract: In this paper,we investigate the impacts of commitment on the market structure and Bertrand competition in the produc-tsupplementary service(PSS)market with information asymmetry.Agame theoretic model is employed to look for the Bertrand-Nash equilibrium in three kinds of market structure with are non-commitment PPS market,unilateral commitment PPS market and bilateral commitment PPS market.With the equilibrium on firm's pricing,profit and market share,it is analyzed that the condition of firm'behavior and its relationship with the market structure and consumer welfare.The results show that:(1)Obviously the equilibrium of the market is different by the effect of firm's commitment to PSS level; (2)Firm's commitmentaction is determined by the distribution interval of PPS level and customer's taste of PSS;(3)The dominant firm always is the leader to of fer commitment,which to the PPS level is maximized as possible as it can;(4)Firm's commitment action increase the PPS level,which is beneficial to consumer welfare.

Key words: produc-tsupplementary service(PSS), information asymmetry, commitment, market structure