The invention provides an engine tail gas after-treatment control system and control method. The engine tail gas after-treatment control system and control method are applied to after-treatment of tail gas. The control system comprises a tail gas post-processor, an engine electric control unit, a diesel injection device, a urea spraying device and a post-treatment electric control single element.The control method is based on the measured values of different sensors and the working condition parameters of an engine, and is based on a pre-calibrated data model to complete the four functions ofDPF active regeneration controlling, DPF accumulated dust cleaning, SCR urea injection controlling and system fault diagnosing. The system is composed of a software system and a hardware system, wherein a transient segmented linear interpolation algorithm is adopted for MAP data, and the calculation precision and the execution efficiency are improved to a great extent. A DPF differential pressuresensor adopts a differential pressure dynamic integral and time-sharing comparison method, so that the condition that the differential pressure value is unstable and the fluctuation is large due to the fact that the differential pressure sensor is influenced by various factors is solved, the robustness of a control strategy of the tail gas after-treatment system is enhanced, and the misjudgment of regeneration is reduced to a great extent, so that the improper active regeneration operation is reduced, and the oil consumption is reduced.