performed by an apparatus for purifying exhaust gas according to various embodiments of the present invention as shown in fig2 the exhaust gas burned in the engine 10 and passing through the turbo charger 20 flows into the cpf device 30 and the cpf device 30 primarily oxidizes the hc the co and the no in the exhaust gas at step s 110 in addition the cpf device 30 regenerates the soot by using the no 2 contained in the primarily oxidized exhaust gas at step s 120 the exhaust gas that is primarily oxidized in the cpf device 30 is transmitted to the doc device 40 through the exhaust pipe 70 and the doc device 40 secondarily oxidizes the hc the co and the no contained in the exhaust gas at step s 130 the loading amount of the noble metal and the ratio of the platinum to the palladium in the doc device 40 are set so as to sufficiently supply the no 2 to the scr device 60 after that the nozzle 50 doses the reducing agent at step s 140 into the exhaust gas that is secondarily oxidized and the exhaust gas is transmitted to the scr device 60 the scr device 60 reduces the no into the n.