The invention discloses a double-seabed-blowout-preventer-stack treatment system and a using method thereof. The double-seabed-blowout-preventer-stack treatment system comprises a tackle travelling rail, a first pressure test room, a first travelling position, a second travelling position, a seabed blowout-preventer-stack crane, a third travelling position, a fourth travelling position and a second pressure test room are sequentially arranged from one end of the tackle travelling rail to the other end of the tackle travelling rail, and a first blowout-preventer tackle is arranged on the first travelling position. A first lower marine riser assembly tackle is arranged on the second travelling position, a second lower marine riser assembly tackle is arranged on the third travelling position, and a second blowout-preventer tackle is arranged on the fourth travelling position. According to the double-seabed-blowout-preventer-stack treatment system and the using method thereof, simultaneous treatment operation of double seabed blowout preventer stacks can be achieved, the requirement that a drilling platform is equipped with the two seabed blowout preventer stacks is met, the efficiency, safety and redundancy of drilling operation are improved, the requirement of the whole system for the transverse size of the platform is low, and the requirement for moonpool openings is low.