The natural gas treatment plant of missan oilfield used the alcohol amine absorption method for desulfurization. In 2023， the natural gas desulfurization unit was blocked， resulting in shutdown. Through the analysis and troubleshooting of the reasons for the blockage of the rich liquid filter， it is determined that the deterioration of MDEA solution causes the blockage of the rich liquid filter， and the reasons for the deterioration of MDEA solution are analyzed. The solutions of filter element replacement and new low-pressure sweet gas pipeline were studied， and the problem of MDEA solution deterioration was successfully solved. After rectification， the iron ion concentration of MDEA solution was normal， the production of the whole unit was stable， the index of exported natural gas was qualified， and the crude oil production of the oilfield was restored to the production before shutdown， so as to ensure the stable production of the oilfield. It can provide reference for similar faults of desulfurization system in natural gas treatment plant.