There are lots of faults in complicated fault block reservoir. And their distributions are quite complicated. Especially in the fault block reservoir with many sub-order faults developed in the fault block，the sub-order faults will influence the water flooding development effect. And the influence rule should be studied to guide flooding pattern deployment and adjustment. According to the distributions and characteristics of the sub-order faults in the complicated fault block reservoir，three flooding patterns were designed and an idealized model of fault distribution was built. Water flooding development effect of different flooding patterns was studied by physical simulation and reservoir numerical simulation. The research results show that development effect of No.3 flooding patterns was the best under the condition of low injection-production pressure drawdown，and No.2 flooding pattern was the best under the condition of high injection-production pressure drawdown. The length of sub-order faults in the fault block will affect the swept volume of the injected water. The longer the fault length is，the larger the unswept reservoir volume of the injected water in the fault block is，and the lower the development efficiency is.