Nowadays, electromagnetic interference (EMI) seems to be one of the major constraints of photovoltaic inverters. Unfortunately, it is too often regarded as the last phase of the development of the system since it represents the last step of its marketing. This paper discusses DC side EMI filter design methodology for photovoltaic inverter system. An analysis of noise source and propagation path impedances of photovoltaic inverter system is conducted. A DC side filter design method is proposed based on the impedance mismatching between the EMI filter impedances and noise source/load impedances. Four different filter topologies are designed and studied. Simulation and experimental results give a firm support to the proposed method.