Air supply system is a significant subsystem of Proton Exchange Membrane Fuel Cell (PEMFC). In order to avoid affecting the service life of the fuel cell, the control objective is to make the oxygen excess ratio of the system track the desired value. In this paper, a robust control method is proposed for the air supply system of PEMFC. Firstly, a differential observer is designed to estimate the cathode pressure. Secondly, in view of the high nonlinearities and measurement noise in the model, an H∞state feedback controller is used to monitor the oxygen excess ratio. Compared with existing control methods for the air supply system, the proposed robust control approach considers disturbances in the model and measurement. In addition, the controller parameters can be rapidly calculated through the convex optimization technique. Finally, simulation results for a PEMFC control system are given to show the robustness of the proposed controller.