The invention provides a virtually expanding imaging device and a method. In a photoelectric collimation and auto-collimation measuring system imaging based on an image sensor, plane mirrors are arranged around the image sensor so as to enable an incident ray outside an original viewing field and inside a new viewing field of the system to be reflected via the plane mirrors, and then to be projected into an imaging face of the image sensor to form light spots, thereby normally imaging the incident ray outside the original viewing field and inside the new viewing field of the system via the image sensor. By adopting the device and the method, the imaging face of the image sensor is virtually expanded without changing the imaging resolution and focus distance, thereby enlarging an incident angle of the incident ray participating in the imaging, and further expanding the original viewing field of the system.