Abstract: Biological technology was used to treat the oil contained in soil from May 4 to Nov. 3, 1998 in Jidong Oilfield. Bacteria and water were added, and the porosity of the soil was enlarged by harrowing and adding slag. The crude oil in the soil could be degraded from 85g/kg to 16g/kg. The daily average degradation rate of the crude oil was 0.15～0.49g/kg.d. When the measures of adding bacteria, water and enlarging porosity was taken at the same time, the crude oil was degraded with best effect. The oil degradation rate is positively correlated with the respiratory intensity of soil bacteria, while the leaching has less impact.