A virtual application program development system, a virtual application installation method, a native API call processing method and a virtual application implementing method are provided to install the virtual application program for performing an application program installing process. A virtual environment library block(20) includes a plurality of modules which processes a native API(Application Program Interface) of the operating system in order to correspond with the virtual environment. If the specific native API is called, it finds the module processing the called native API as described above among a plurality of modules and the virtual environment library block operates. A virtual application installed block(10) receives the location information of the application virtualizing from the user and 'the information of the installation place setting up the virtualized application. The virtual application installed in the virtual application program performance block(30) is the installation place.