An exhaust gas purification system of engine configured to classify a PM accumulation state of DPF into multiple evaluation stages based on a plurality of evaluation indices, and to repeatedly perform determination of the current evaluation stage by the current stage determination part and determination of whether to move up the current evaluation stage to the evaluation stage of the next rank by the evaluation stage determination part, wherein upon a defect of a sensor among different types of sensors being detected by the defect detection part, the current evaluation stage is newly redetermined by the current stage redetermination part as substituted for the current evaluation stage determined by the current stage determination part.