A pseudo H&E image producing method, including: inputting a grayscale interference image or a grayscale reflected image of a pathological sample to a first memory block of an information processing apparatus, and inputting a grayscale fluorescence image of the pathological sample to a second memory block of the information processing apparatus; using the information processing apparatus to perform a first color transform operation on the grayscale interference image or the grayscale reflected image to generate a first RGB image, and using the information processing apparatus to perform a second color transform operation on the grayscale fluorescence image to generate a second RGB image; and using the information processing apparatus to perform an image fusion operation and an intensity reversal operation on the first RGB image and the second RGB image to generate a pseudo H&E image. The present invention also discloses an optical system using the method.