To protect transaction safety is the fundamental function of guarantee law. With the development of market economy, the guarantee law develops an additional function ,namely economic promotion function. With the guarantee law's economic promotion function , goverment can establish certain security institutions to help those important vunerable industry or vulnerable groups to obtain capitals.Thus, security institutions is divided into two kinds. One is devoted to secure certain transaction safety, while the second aims to promote some important vulnerable industry and groups' ability of providing guarantee, and then promotes rapid economic development. The first kind of security institutions are called fundamental guarantee, while the second kind are named policy-based guarantee, for their obvious policy objectives. As the means of macro-control, policy-based guarantee has great advantages, and it's appplication varies with the development of economy and government policy. Thus, The paper researches merely on the application of policy-based guarantee's in small and medium-sized enterprise, security of housing consumption for the disadvantaged, construction of infrastructure and agriculture financing.The dissertation is divided into five chapter:Chaper Ⅰ, on basic theory of policy-based guarantee. First, based on the function of economic promotion, guarantee can be used as macro-control by government to promote certain vulnerable industry or groups, which is called policy-based guarantee. Policy-based guarantee plays role in allocating resources, allocating income, adjusting struction of industry, and has more advantages than other macro-control method. Policy-based guarantee can easily be adapted to the marketizing tendency of macro-control, conveys the government's economic policy, also it is convenient than administrative method. However, policy-based guarantee has negative effect on economy, mainly due to the asymmetry information among government , guarantee orgnizations, borrower. Thus, measures must be taken to perfect policy-based gurantee in order to dominate its negative effect. Guarantee law belongs to the branch of promotion economic law, mostly regulating by interest inducing, instead of administrative regulating.Chaper Ⅱ, on SMEs' (Small and Medium-sized Enterprize) credit guaruatee. Small and medium-sized enterprize plays important role in increasing employment,