Rectifier substations in DC electric transportation systems are an important source of harmonic distortion. One of the best compensation actions is to use active power filter due to its adaptation capacity to different load conditions. This paper presents a computational model of DC traction supply systems that allows the presentation of the current distortion in the distribution system under several traction load cases. The compensation is developed using active power filter with a control system based on the p-q theory. Simulations without and with active compensation shows the effectiveness of active power filter in DC traction systems.