Abstract: A long-term investigation has been made on inter-planting effects of 3 types of densities regarding tree-grass combination on the saline-alkaline soil irrigated with sewage from sewage treatment plants of the petroleum industry.Both tree species and grass species suitable for long-term inter -planting have been screened.In addition,based on analysis and evaluation of densities(spacing between rows and individuals),models and effects of long-term inter-planting of trees and grasses,the optimal inter-planting density and mode have been suggested.At the same time,effects for extending inter-planting of trees and grasses on 3 different types of soil were analyzed and summarized.