EXHAUST GAS PURIFICATION SYSTEM AND EXHAUST GAS PURIFICATION METHOD

An exhaust gas G of an internal combustion engine 11 is made to pass through an exhaust gas purification device 20 after passing through a pre-oxidation catalyst 25, and when a first temperature T1 of the exhaust gas G on an upstream side of the exhaust gas purification device 20 is lower than a first set temperature T1c, multistage temperature rise injection is performed, while when the first temperature T1 becomes the first set temperature T1c or more, post injection is performed in addition to the multistage temperature rise injection, and feedback control of the post injection is executed so that a second temperature T2 of the exhaust gas G on a downstream side of the exhaust gas purification device 20 becomes a second set temperature T2c. As a result, by installing the pre-oxidation catalyst 25 on an upstream of the exhaust gas purification device 20 including a pre-stage oxidation catalyst 21 and by controlling fuel injection in the multistage temperature rise injection and the post injection, improvement of Nox purification characteristics at a low temperature, prevention of generation of white smoke caused by HC slip in DPF regeneration at a low temperature and the like are realized.