Dynamic response performance of PEMFC affects its durability and reliability significantly. So improving on dynamic performance of PEMFC has become the key for prolonging PEMFC life in fuel cell vehicles application. In this study, in order to promote the PEMFC dynamic response performance, RuO2·xH2O was prepared by solgel method and then sprayed onto catalyst layers. The RuO2·xH2O prepared was characterized by TEM, which shows the average particle size of RuO2·xH2O was 8 nm and particulates were well distributed. A 10-cell stack using MEAs with and without RuO2·xH2O was assembled and studied under different relative humidity. It was found that added with RuO2·xH2O dramatically improves the dynamic response performance, which revealing that RuO2·xH2O can buffer the voltage undershoot and improve the stability and lifetime of PEMFC stack.