The biggest problem of the wet-desulfurization which be used to semi-water gas desulfurization in synthetic ammonia industry was the resistance of thionizer. The increased resistance of thionizer was mostly caused by the accumulation of secondary salt or sulfur paste that cloged liquid channel.The content of secondary salt-sodium hyposulfite was detected using iodometry, and the corresponding relationship between the fluctuation of the content of sodium thiosulfate in desulfurization solution and the resistance of thionizer were proved by unremittingly long-term monitoring, tracking and contrasting, the occurrence of thionizer sulfur blocking were prevented, and strong protection for the desulfurization system's safe, stable, long-period operation were provided by capturing signs of thionizer resistance increase or desulfurization solution composition deteriorate in time, and taking targeted preventive measures .