The present invention makes it possible to cope with a plurality of standardized transient operation modes in a method for adapting the engine transient characteristic to a required performance targets and a system therefore. When there are a plurality of prescribed standardized transient operation modes, transient testing is conducted in a single transient operation mode that covers changing patterns of control values of control factors of the plurality of transient operation modes. Only data in a data distribution range to be focused on is captured to create a transient engine model.