Prepayment option and default option are implied in the housing mortgage loan, but whether they will be carried out depends on two risk factors, which are interest rate and housing price. Traditional structured option pricing theory usually overestimates the option value of housing mortgage loan. The double binomial tree quid pricing model makes it better adaptive by taking multi-step jumping cases into account on the basis of model Wei, combining HST model to remove state variables' correlation and by introducing social cost as a variable. The empirical analysis indicates that the option value increases sharply when housing price fluctuates to a certain extent, and interest rate fluctuation influences the option value directly or indirectly by affecting housing price. Therefore, it is necessary to pay great attention to the impact of interest rate on real estate market, and to strengthen the macro-control on real estate market in order to maintain its healthy development.