Metamaterial amplifying device can make an object enlarged as one desire, and its potential application to small object identification and detection is foreseeable. To facilitate the practical application of such a device, a new simplified parameter designing method is proposed through choosing appropriate transformation equation based on the theory of transformation optics. The virtues of such a method are that not only the radial and azimuthal parameters are constants and only axial parameter varies with radius, but also, there exist no undesired reflections due to perfect impedance matching to free space at outer boundary. Fullwave simulations confirm the effectiveness of the proposed method and the good performance of the designed amplifying device. Moreover, the effects of material loss and parameter deviation on the performance of the device are also investigated. This work expands the application of transformation optics, and also provides a new and feasible solution to simplify the parameters of metamaterial devices.