There exists the information asymmetry between banks and enterprises that need loan, which can cause the problem of adverse selection. With the symmetry information, banks and enterprises can manage to reach best contracts. However, with the information asymmetry, when banks select the price of loan according to the average risk level of borrowers, the problem of adverse selection appears. Mortgage and guarantee are all very helpful to deal with adverse selection in some sides. For example, guarantee can send a signal to banks that enterprises could be low risky, and mortgage can make highly risky enterprises give up borrowing since it will bear more responsibility for its fail. A form of contract that connects the price of loan with the value of mortgage can help to recognize the style of different borrowers.