Proposed is a pretreatment desulfurization system including: a first chute for supplying a pretreatment apparatus with coal transported by a belt conveyor; a pretreatment apparatus for immersing the supplied coal in a catalyst mixture obtained by mixing a desulfurization catalyst and water, thereby desulfurizing the coal; a mesh conveyor for separating the coal being immersed in the catalyst mixture and having passed through the pretreatment apparatus, into a liquid phase and a catalyst-treated coal; a mesh conveyor for transporting the catalyst-treated coal; and a storage tank for storing the transported catalyst-treated coal.