A dual controller storage apparatus and a cache memory mirror method thereof are described. The storage apparatus includes a imaging environment module, a storage device, a first controller, and a second controller. The first controller has a virtual disk and a first cache memory. The second controller has a second cache memory. The present invent provides a imaging environment function to select the first or the second controller to serve an extranet according to the request of the extranet. If the imaging environment function selects the second controller, the data received from the extranet is written into the second cache memory. Communication between the second controller and the first controller is established, and the data of the second controller received from the extranet into the first cache memory and the virtual disk.