The pyrophoric iron sulfides in oil tank was eliminated under THPS(tetrakis(hydroxymethyl)phosphonium sulfate) and ammonium chloride. It was investigated the effect of mass ratio of THPS and ammonium chloride，the concentration and acidity of dissolution agent, temperature， and reaction time on the efficiency of dissolution. The results show that the efficiency of dissolution to iron sulfide is best when mass ratio of THPS and ammonium chloride is 6.5∶0.6,temperature is 80 ℃, pH is 5, reaction time is 8 h, the dissolution of iron sulfide is best. When the concentration of dissolution agent is 14.0%, the efficiency of dissolution to iron sulfide is reach 92.50%.