The invention belongs to the technical field of tunnel illumination, in particular to a tunnel natural light and traditional lamp combination illumination system and an illumination method. A light guide device is utilized to introduce sunlight into a tunnel to be combined with traditional illumination lamps for illumination. A lighting part is arranged outside a tunnel and is used for collecting natural light, and a light scattering part is arranged in the tunnel and is used for enabling the natural light collected by the lighting part to illuminate in a scattering manner. A light guide device is arranged to connect the lighting part with the light scattering part and is used for guiding the natural light collected by the lighting part to the light scattering part, and the light scattering part is arranged at the position of the traditional illumination lamps. A traditional illumination part is provided with a control part to control the turn-on and turn-off of the traditional illumination lamps, and the control part can control the quantity of the traditional illumination lamps turning on and turning off according to the strength of the natural light outside the tunnel. The illumination time of the traditional lamp is shortened, and the illumination cost is effectively reduced. The tunnel natural light and traditional lamp combination illumination system can effectively overcome the conventional technical defects and has the advantages of being wide in range of application, low in cost, simple in technological realization and environmental-friendly.