An exhaust gas post-processing apparatus comprising: a selective catalyst reduction device provided in an exhaust gas line; a diesel oxidation catalyst device disposed at an upper stream than the selective catalyst reduction device; a first sensor being provided at an upstream of the diesel oxidation catalyst device to measure nitrogen oxides contained in the exhaust gas; a second sensor being provided at a rear end of the selective catalyst reduction device to measure nitrogen oxides contained in the exhaust gas; a third sensor being provided at the upstream of the diesel oxidation catalyst device to measure a back pressure of the exhaust gas; a fourth sensor which detects a temperature of the exhaust gas at the upstream of the selective catalyst reduction device; and a control unit which calculates a reduction efficiency of nitrogen oxides by a difference between a concentration of the nitrogen oxides detected in the first sensor and a concentration of the nitrogen oxides detected in the second sensor to send a control command to increase the temperature of the exhaust gas when the reduction efficiency is lower than a predetermined reduction efficiency, wherein the control unit is configured to increase the temperature of the exhaust gas until the temperature of the exhaust gas detected by the fourth sensor reaches a target temperature, and determines whether a back pressure of the exhaust gas measured by the third sensor at the upstream of the diesel oxidation catalyst device in the exhaust gas line reaches a predetermined back pressure and sends a control command to increases the temperature of the exhaust gas when the back pressure reaches the predetermined back pressure. a selective catalyst reduction device provided in an exhaust gas line; a diesel oxidation catalyst device disposed at an upper stream than the selective catalyst reduction device; a first sensor being provided at an upstream of the diesel oxidation catalyst device to measure nitrogen oxides contained in the exhaust gas; a second sensor being provided at a rear end of the selective catalyst reduction device to measure nitrogen oxides contained in the exhaust gas; a third sensor being provided at the upstream of the diesel oxidation catalyst device to measure a back pressure of the exhaust gas; a fourth sensor which detects a temperature of the exhaust gas at the upstream of the selective catalyst reduction device; and a control unit which calculates a reduction efficiency of nitrogen oxides by a difference between a concentration of the nitrogen oxides detected in the first sensor and a concentration of the nitrogen oxides detected in the second sensor to send a control command to increase the temperature of the exhaust gas when the reduction efficiency is lower than a predetermined reduction efficiency, wherein the control unit is configured to increase the temperature of the exhaust gas until the temperature of the exhaust gas detected by the fourth sensor reaches a target temperature, and determines whether a back pressure of the exhaust gas measured by the third sensor at the upstream of the diesel oxidation catalyst device in the exhaust gas line reaches a predetermined back pressure and sends a control command to increases the temperature of the exhaust gas when the back pressure reaches the predetermined back pressure.