Abstract: A model of optimal decision on fortification intensity for natural gas pipeline network is established, taking the sum of construction cost of natural gas pipeline network, failure loss expectation of pipeline structure in future seism and failure loss for services after the disaster as minimal objective function, combined with the restrictions of project investment, aseismatic reliability for pipeline network and special requirement of fortification for partial pipelines. The cubical algorithm for disjoint of Boolean function that is applicable for reliability calculation of network system is used as the tool of aseismatic reliability analysis for multi-source and multi-terminal network system. Combined with reproduction strategy of differential evolution algorithm with the cross and variation of genetic algorithm, a new hybrid genetic algorithm is applied to the optimization solution for fortification intensity of natural gas pipeline network. Taking a natural gas network as an example, under a condition of seven magnitude seism, a decision of optimal fortification intensity for gas pipeline is made and corresponding results are given meantime.