A testing device is provided to include a pre-boot execution environment (PXE) server, a dynamic host configuration protocol (DHCP) server, and a computer. The computer is connected to the PXE server and the DHCP server via a network. The PXE server includes an image file stored therein, a communicating module of server terminal and a communicating module of client terminal. The computer includes a network device for supporting PXE functions. A testing method is provided to include following steps: connecting the PXE server and the DHCP server to the computer via the network, the DHCP server assigning an IP address to the computer, the computer downloading the communicating module of client terminal from the PXE server, for communicating with the communicating module of server terminal, and the image file being run to test the computer.