Embodiments of the invention provide a method, a device, and a system for optimizing application programs. The method comprises: obtaining a to-be-optimized application program installation package suitable to be used for a mobile terminal, obtaining an executable file used for installation of the application program from the application program installation package; injecting a dynamic library which is generated in advance to be used for bearing custom code tools into the executable file; embedding a new description file used to replace an original description file into the executable file; resigning the executable file which includes the dynamic library and the new description file; packaging the executable file which is resigned, to obtain an optimized application program installation package; the optimized application program installation package being used to install an optimized application program on a mobile terminal. The method, the device, and the system can simply and conveniently realize optimization of application programs under the condition that preinstallation of APPs is not needed, and complicated analysis processing is not needed, and the method, the device, and the system saves time, efforts, and are efficient.