This paper studied the nutrient balance and mechanism for enhancing the bioremediation of petroleum contaminated soils by the bio-slurry method. Oil degrading strains isolated and screened from Liaohe oil field was used. The results show that the suitable weight ratio of N and P element in the nutrient is 5.67:1, which is similar to their proportion in the microbial cells. It was found that the degradation of oil was significantly enhanced by adding nutriment and about 30% oil was decreased in the 14,000 mg/kg-15,000 mg/kg samples during 16 days. Using (NH4)2SO4, NH4NO3, NaNO3, CO(NH2)2 as the nitrogen source respectively, it shows that the inorganic nitrogen is better than the organic one, and the nitrogen in nitrate is more effective than that in ammonia. Adding nutrient salt can change the system's pH and promote the growing of the microbes.