The invention provides a computer system and a method for testing hardware device based on virtual machine. The computer system comprises a virtual machine device installed with a guest operating system. The guest operating system comprises a guest driver and a hypervisor having an expansion test module. When the computer system is intended for testing the hardware device, the guest driver will issue a sequence of test instructions to a real hardware or a virtual hardware via the expansion test module. The real hardware or the virtual hardware processes the test instructions so as to generate at least one response signal and transmit the response signal to the guest driver via the expansion test module. The guest driver is capable of detecting the response signal in order to verify the correctness of the real hardware or the virtual hardware processing the test instructions.