Ｒecently，Chinese corporations are constantly disturbed by external and internal unexpected events，such as US financial crisis，European debt crisis，snow disasters and earthquakes，which make the asset values plummet in a short time and thus cause the high default rates of corporate loans． Obviously，the existing diffusion-process based default models can not illustrate this kind of jump risk． This paper tries to introduce the jump factor into the First-Passage time model and discusses how jump risk impacts on corporate default rates when the default threshold keeps constant or changes． In addition，this paper analyzes the asset structure of corporations，derives the non-linear relation between equity value and asset value and provides the methods estimating the parameters in the model．