The invention relates to a hidden anchor cantilever beam type comb tooth bridge expansion device which comprises two comb tooth plates respectively arranged on bridge members on two sides of an expansion joint. Comb teeth of the two comb tooth plates are inserted in a staggered way, vertical stiffening ribs are connected to the bottoms of the comb teeth and form a cantilever beam type structure, and the cantilever beam type structure is fixed to the bridge members on the corresponding sides through anchor pulling plates and hidden anchors. The anchor pulling plates are fixedly connected with the fixed ends of the comb tooth plates on the corresponding sides and the corresponding vertical stiffening ribs respectively, and are welded with steel bars in the bridge members on the correspondingsides. The vertical stiffening ribs are arranged at the bottoms of the comb tooth plates and combined to form the cantilever beam type structure, so that the comb tooth expansion device is transformed into a beam type structure system from a conventional plate type structure system, the section inertia moment and the section rigidity of the expansion device can be effectively increased, and the service life of the expansion device is prolonged.