The present invention provides a method for controlling regeneration of the simultaneous NOx-PM reduction apparatus having a lean NOx trap (LNT) for removing nitrogen oxide (NOx) an engine and a catalytic particulate filter (CPF) for trapping a particulate matter (PM) of the engine. According to an exemplary method, depending on the trapped PM amount in the CPF, the simultaneous NOx-PM reduction apparatus is regenerated according to a dual step regeneration including a mild regeneration at a low CPF interior temperature and a strong regeneration at a high CPF interior temperature.