The function of consumption pattern is established and the resident consumption pattern is analyzed, which accords with the assumption of life period. The necessity for resident to use housing mortgage loan is discussed. The avail function of clearing off the residential housing mortgage loan and the condition which can make the best avail of clearing off mortgage loan are built up. Based on the above mentioned built up condition, a method to calculate the price of house which one can afford or the period of clearing off mortgage loan at different structures of clearing off is presented and the factors which influence the price or the period are analyzed. Finally, with certain supposition, the different prices of houses at different ways of clearing off the mortgage loan, for example, constant payment mortgage, geometric proportion increasing payment mortgage and geometric proportion descending payment mortgage are calculated.