The present disclosure relates to an exhaust gas post-processing apparatus, and more particularly, to an exhaust gas post-processing apparatus and a control method thereof which reduce emission of nitrogen oxide (NOx) by bypassing high-temperature exhaust gas to a front end of a selective catalytic reduction. Accordingly, some embodiments of the present disclosure have been made to solve one or more of the aforementioned problems, and some embodiments of the present disclosure increase a reducing rate of nitrogen oxide by controlling a flow of exhaust gas by changing a structure of an exhaust pipe. The exhaust gas post-processing apparatus and the control method thereof according to the present disclosure may increase a reducing rate of nitrogen oxide.