The present invention provides an image sensing device and an optical diaphragm thereof. The image sensing device comprises a substrate, a light sensing circuit, an optical diaphragm and a light source. The substrate has first and second surfaces that are opposed to each other. The light sensing circuit is provided on the first surface. The optical film is disposed on the second surface. The light source is disposed on the side of the optical film facing the substrate. The optical diaphragm has a transparent film body and a grating structure. The transparent film body has opposing first and second faces. The light transmittance of the light transmission film for the red light band is greater than the light transmittance for the blue light band. The grating structure is arranged on at least one of the first and second surfaces, and the light transmittance of the grating structure is smaller than the light transmittance of the light transmissive film body. The invention can help improve the image clarity by increasing the transmittance of the long wavelength visible light band through the optical diaphragm.