The invention belongs to the field of environmental engineering and relates to a semi-dry-process desulfurization apparatus. The apparatus comprises an inlet of an absorption tower, a guide plate, a dense phase chamber, a circulating fluidization chamber, a partition plate, an ash bucket and an outlet of the absorption tower, wherein the absorption tower is of a U-shaped design; the inlet of the absorption tower is arranged at the upper part of the left outer side of the whole apparatus; dust-containing flue gas enters the dense phase chamber from the inlet of the absorption tower via the guide plate; the flue gas and a desulfurizer are subjected to contact reaction in the dense phase chamber; large-grained circulating ash after reaction directly falls into the ash bucket at the bottom of the absorption tower, and fine-grained circulating ash enters the circulating fluidization chamber to be subjected to further reaction along with the flue gas; the desulfurized flue gas and part of the fine grains enter a subsequent dust remover from an outlet of a desulfurization tower; and the circulating ash at the bottom of the absorption tower and in the ash bucket of the dust remover is lifted to the inlet of the absorption tower in a medium-pressure delivery manner, thus finishing the whole cycle. According to the invention, the desulfurization reaction time is increased, the desulfurization efficiency is improved, the amount of the circulating ash is reduced, the load of the dust remover is lowered, the service life of the dust remover is prolonged, the energy is greatly saved, and the maintenance and repair frequency of the apparatus is reduced.