The invention discloses a metal roof plate and plane tile combined roof system and a construction method thereof. The method comprises the following steps that a plurality of longitudinally and transversely staggered purlines are arranged on a roof steel structure of a building structure, and the upper surfaces of the plurality of purlines are controlled in the same plane; a bottom plate is arranged on the roof steel structure, and is fixed on a side surface support plate of the plurality of purlines; a dustproof layer, a sound absorbing layer and a steel wire net are sequentially paved on the bottom plate; an aluminum alloy support frame is arranged in a position, corresponding to the longitudinally and transversely connected position, on the steel wire net; a heat insulation layer and a waterproof ventilated membrane are sequentially laid on the steel wire net; the lower part of the aluminum alloy support frame is embedded in the heat insulation layer and is fixed with the purlines; the upper part of the aluminum alloy support frame is exposed out of the waterproof ventilated membrane; a metal roof plate is arranged on the waterproof ventilated membrane, and is fixed at the upper part, exposed out of the waterproof ventilated membrane, of the aluminum alloy support frame; a connecting device is arranged on the metal roof plate; and plane tiles of a tiled roof are arranged on the connecting device.