The efficient and reliable operation of oil field water injection pipe network system is very important in the product of oil field.The paper used the method of double network mutual backup and applied water injection pipeline theory,graph and optimization theory so as to improve the reliability of two tree-type networks with as little cost as possible. In the connected case of a single tube and double tube,the paper compared reliability of two networks and the cost of connection section in two states with pressurized equipment and non-pressurized equipment. The results show the reliability of two tree-type networks is higher in the case of double tube connection with pressurized equipment.Finally the optimized connection scheme is achieved between two tree network topologies which ensures the high reliability of system.