Disclosed are an apparatus and method for diagnosing an abnormality of a mobile communication network. The apparatus for diagnosing an abnormality of a mobile communication network includes a modeling unit that models a control plane operation of an analysis target mobile communication network based on a control plane messages collected by a preset Mobile Network Operator to a terminal in a formal model of a form of a state machine, an analysis unit that compares processing required times of a control plane operation model of the modeled analysis target mobile communication network and a control plane operation model of another mobile communication network previously generated in a same path, and a detection unit that detects an abnormal operation of the mobile communication network of the analysis target based on a comparison result.