The invention belongs to the field of wet desulphurization. The invention in particular relates to a low-cost desulfurization wastewater zero-discharge system for improving gypsum quality. A concentration tower and an absorption tower are connected in series; flue gas heat can be effectively utilized, filtrate water from a gypsum vacuum belt dehydrator is concentrated through low-temperature fluegas in a concentration tower, the problem of zero emission of desulfurization wastewater is solved by using a low-cost method under the condition of ensuring high-index operation of an absorption tower, and high salinity contained in the desulfurization wastewater is treated in a solid form through a concentration crystallization mode, so that the subsequent treatment difficulty is reduced; afterslurry discharging and filter pressing of the concentration tower, acid filtrate with the pH being about 2 is extracted and dechlorinated, then limestone is dissociated, limestone slurry is graded, and high-quality gypsum low-cost desulfurization wastewater zero-discharge system is remarkable in effect, simple in structure and low in investment and operation cost, can bring remarkable economic benefits to enterprises, and has good environmental and social benefits.