针对质子交换膜燃料电池PEMFC（proton exchange membrane fuel cell）系统的强非线性及强耦合特性，提出一种适用于PEMFC系统过氧比OER（oxygen excess ratio）估计的鲁棒非线性系统观测器 ，解决PEMFC系统中难于利用传感器直接测量的状态变量（e.g., air mass in the sup鄄ply manifold, oxygen mass and nitrogen mass in the cathode side） that cannot be directly measured by sensors in the PEMFC system. Through matrix transformation, the differential mean value theorem is used to transform the dynamic er鄄ror system into a linear variable parameter system. Based on the Lyapunov stability theory and convexity principle, the observer design problem is transformed into a linear matrix inequality（LMI） feasibility problem. Simulation results show that the designed observer has satisfying convergence characteristics.