Abstract: Under simulated experiment in laboratory,the degradation characteristics of metam sodium and methyl isothiocyanate and their influencd factors were investigated in soil by using high performance liquid chromatography (HPLC).The degradation rate of metam sodium in soil relates to the water content,temperate and organic carbon level.When at soil temperate of 20 ℃,the half-lives of metam sodium were 5.0,1.2,4.1 and 4.3 days in soil containing 0,20%,40%,60% water,respectively.The result indicated that the degradation velocity of metam sodium was the fastest in soil with 20% water content.The degradation rate of metam sodium in soil increased with higher temperature and organic carbon level of soil.The degradation trends of methyl isothiocyanate and metam sodium are similar.The current result provided useful information for safety application of metam sodium in field use.