During the development process of international investment law, the initial meaning of protecting foreign investors equals to protecting them from illegal expropriation by the host countries. The trend of investment liberalization is marked with and resulted from the conclusion of most BITs and some important regional investment treaties since nineties of the 20th Century, the existing of all the stereotype expropriation clauses have confirmed the principle that host countries must compensate the foreign investors due to expropriation. The problem concerning compensation standard, which is once sensitive and disputable, has also led to a specific and unanimous answer. The composition and finding of expropriation are much clear for a long period of time. However the answer becomes unclear again with the rapid expansion of expropriation concept. The modern investment treaties define the expropriation clause in three forms, direct expropriation, indirect expropriation and any measure equivalent to or similar to expropriation. Although it is held that the so called “equivalent to or similar to” do not create the third form of expropriation, the expression of indirect or similar expropriation will continue to be widely used and will expand the concept of expropriation in an effective way. The expropriation clause has become the first choice for the investors to claim the host country for compensation. The claims of indirect expropriation have been regarded as a threat to the regulation power of host country in the current international law. And the inconsistent findings of disputes mean uncertainties both to the foreign investors and the host countries. If the balance between the protection over investor property and the regulation power of the host country cannot resolved thoroughly, it will undoubtedly endanger the application and development of expropriation clause in