DDT was a pesticide commonly used to kill insects. it has been banned because of high toxucity and long term persitent. However, currently DDT residues for a long time in soil and water under old storage causing great toxic to humans. This paper shows the effectiveness of some factors on DDT treatment by Fe nano. When treating DDT residue in artificial polluted water with DDT at 35 mg/l, by the ratio of Fe nano/DDT is 19/1 at pH = 3, the efficacy to decompose DDT for 24 hours is 82.51 percent, higher than the efficacy when treating at pH = 7 (69.74 percent). For Huong Van soil whose DDT is 0.978 mg/kg, the ratio of Fe nano/DDT is 205/1 then after 10 days, all the DDT in soil is totally treated. With the ratio of Fe nano/DDT is 4/1 after 20 days, DDT can be treated to 78 percent. At pH = 3 the effectiveness of DDT treatment is highest humic acid inhibited the reduction of DDT. The treatment efficacy of DDT decreased from 78 percent to 20 percent when adding 50 percent humic acid.