The invention provides an emission post-treatment system applied to a methanol engine, and relates to the field of tail gas treatment. The emission post-treatment system comprises an exhaust gas recirculation unit, a three-way catalyst and a calibration unit; the exhaust gas recirculation unit is used for feeding part of tail gas generated by the engine back to a cylinder so that the nitrogen andoxygen compounds in the tail gas can be reduced and the fuel consumption rate can be increased by changing the combustion temperature and the oxygen concentration of the mixed gas in the methanol engine cylinder; the three-way catalyst is used for treating the tail gas to enable the components in the tail gas to reach the preset standard through the catalyst; and the calibration unit is used for enabling the combustion air-fuel ratio to be kept in a preset range taking the theoretical air-fuel ratio as the center through calibration and adjustment on the basis that the operating condition of the methanol engine is stable. According to the emission post-treatment system, the methanol and formaldehyde specifically owned by the tail gas of the methanol engine can be deeply converted; and compared with an original emission post-treatment system, the cost is reduced, and the treatment effect is improved.