Abstract: A dark field illuminator for microscopic imaging is provided. The dark field illuminator is arranged above an adjustable lens group of a unit microscopic imaging module and corresponds to the adjustable lens group, a surface of the dark field illuminator is attached to a back of a sample slide, and the sample slide is located between the dark field illuminator and the adjustable lens group; the dark field illuminator includes a bright and dark field substrate and a dark field black background patch, the size of the dark field black background patch matches with that of the adjustable lens group, and the dark field black background patch is arranged close to or away from the adjustable lens group relatively to the bright and dark field substrate. Preferably, the bright and dark field substrate further has a recessed structure with a white diffuse reflection surface.