The invention relates to a novel assembly type seamless expansion device and a construction method thereof. The novel assembly type seamless expansion device comprises main girder span expansion device bodies arranged on a construction bridge and expansion device bodies arranged on the portions, at bridge abutment expansion seams, of bridge abutments of the construction bridge, and each main girder expansion seam and each bridge abutment expansion seam are each provided with one expansion device body. Accordingly, the device and a deck can be paved to form a continuous whole body, the problemsthat bridge expansion seams are prone to bridge surface roughness, dislocation, distortion, expansion seam irregularity and the like can be solved, and driving is stable and comfortable; by arrangingrubber pads between comb type span seam steel plates and telescopic corrugated steel plates, driving noise can be reduced, the defects that traditional expansion seams are prone to leakage, and the service life in bad conditions is short can be overcome, and the maintenance workload is low. In addition, the device has the advantages that the input cost is low, the stress performance is good, thedurability is good, the practicability is high, and maintaining and replacing are conducted conveniently.