A purification system for variable post injection in LP EGR, the system includes a turbo charger disposed downstream of a diesel engine, a DPF (catalyzed particulate filter) disposed downstream of the turbo charger, a NOx reduction apparatus disposed upstream or downstream of the DPF, a bypass line diverged from the DPF for mixing exhaust gas and air inflowing the turbo charger, a exhaust gas control portion disposed downstream of the DPF for controlling flowing of the exhaust gas and a lean/rich controlling portion for controlling lean/rich of the exhaust gas.