The invention discloses an automatic paralleling method and device for steam-driven induced draft fans of a thermal power generating unit. The method comprises the steps of: determining whether automatic paralleling of steam-driven induced draft fans is required according to unit load; when automatic paralleling of steam-driven induced draft fans is required, controlling stationary blades of an electrically-driven induced draft fan to automatically track and maintain stable furnace draft of the thermal power generating unit, carrying out a paralleling operation to the steam-driven induced draft fan A and the steam-driven induced draft fan B in the thermal power generating unit in order, adjusting the steam-driven induced draft fan A and the steam-driven induced draft fan B to be identical in rotating speed and stationary blade opening, and controlling the stationary blades of the steam-driven induced draft fan A and the steam-driven induced draft fan B to automatically track the furnace draft. The device comprises an automatic paralleling trigger unit, an automatic control unit for the electrically-driven induced draft fan, a first paralleling operation control unit, a second paralleling operation control unit, a synchronous operation control unit for the steam-driven induced draft fans, all of which completely correspond to the method. The automatic paralleling method and device for the steam-driven induced draft fans of the thermal power generating unit allow decrease of fan paralleling time, reduction of manual operation, and reduction of risks of stalling and surging during fan paralleling.