This essay illustrates the importance of credit to the supply of asset pool and the operation of MBS from the accept and the basic operation process of MBS. According to our country's conditions, this essay states from two sides. Through the game of housing consumer and commercial, for one thing, housing consumer desides applying for loan or not,and commercial bank desides granting loan or not; for another ,housing consumer selects prepaying loan,paying loan on time or branking contract,and commercial bank selects lawsuiting or not. Through the game analysis of two sides , it discusses relations between the loan of bank and the development of credit system,and give us some suggestions in order to the development of MBS.