An operating method for an interactive writing device is provided. The operating method includes following steps. A visible light image is captured in response to an original outputted image. A tag searching region is established in the visible light image in response to a writing operation performed by a writing object having a color tag pattern. The original outputted image corresponding to the tag searching region is filtered from the visible light image in the tag searching region to generate a local processed image. A color tag corresponding to the color tag pattern of the writing object is searched from the local processed image. A color value corresponding to the color tag is generated.