The invention discloses an internal diagnostic device of the oral cavity, which includes a handle and a lens. The invention is characterized in that the lens is connected with the handle by a lens frame; an LED is arranged on the lens frame; a power source is arranged in the handle; the power source and the LBD are connected by a lead; a switch is arranged between the LED and the power source. The diagnostic device has the beneficial effects of integrating a lighting lens and an endoscope into a device which not only can observe the situation of the inside of the oral cavity by the lens, but also can provide illumination, thus being capable of clearly observing the internal tissues of the oral cavity.