The traditional PMU placement methods may be unable to observe the power system under the N -1 condition， while PMU placement methods fully considering the N -1 condition need too many PMUs to ensure the observability of entire power system. In order to overcome the shortcomings of the above methods， this paper presents a PMU placement method with better cost-benefit ratio. It is based on the principles of Taguchi robust design method. Based on the complex network theory， a set of integrated vulnerability indices calculated by complementary vulnerability index set are used to identify the important lines in the system. By doing so， the aim of the design is focused on ensuring the important lines' observability and the robustness of the placement plan under the N -1 noise. In the design， the Taguchi quality characteristic and the signal noise ratio indices are calculated to measure the PMU placement plan's observability capabilities and robustness under the N -1 noise. Finally， a two stage optimization procedure is used to determine the final plan. A sample system is used to test the performance of the PMU placement plan， and the results show that the method is very effective and practical.