After investigation of pollution of a certain irrigation area, and analysis of various methods for treating polluted soil, a technique was put forward using microbial preparation and mycorrhiza to remedy polluted soil. Experiment results showed that microbial preparation made in lab has a rewarding effect on decreasing oil pollution of the soil. With soybean and corn, fungi can grow with plant root into micorrhiza, which as a bioremediation method is effective and economically in treating soils contaminated by petroleum hydrocarbons. Using this technique we can remedy sewage irrigated areas by 53~78%, which indicated that a technological basis will be available for bioremediation of soils contaminated by petroleum hydrocarbons.