An assembly method of direct-docking probing device is provided. First, a space transforming plate made by back-end-of-line semiconductor manufacturing process is provided, so the thickness of the space transforming plate is predetermined by the client of probe card manufacturer. Then a reinforcing plate in which a plurality of circuits disposed is provided, which has larger mechanical strength than the space transforming plate. After that the reinforcing plate and the space transforming plate are joined and electrically connected by a plurality of solders so as to form a space transformer. Then, a conductive elastic member and a probe interface board are provided. Thereafter, the space transformer and the conductive elastic member are mounted on the probe interface board. After that, at least one vertical probe assembly having a plurality of vertical probes is mounted on the space transforming plate, and the vertical probes is electrically connected with the space transforming plate.