The invention provides a diesel engine aftertreatment SCR control device and method. The control device comprises an SCR controller, an engine, an exhaust pipe, a catalyst device, a metering pump, an NO<x> sensor, a urea tank, an upstream temperature sensor, a downstream temperature sensor, a nozzle, a cooling water control electromagnetic valve, a water supply pipeline, a heating pipeline, a urea solution pipeline, an instrument and an OBD diagnosis device. According to the diesel engine aftertreatment SCR control device, the system reliability, safety and the compatibility can be improved, and the low energy consumption function is achieved; the system signal collection precision and stability are improved, and therefore the urea injection amount control precision is improved; the system power output reliability is improved; the device can be compatible with different commercial vehicle instrument connectors, analog and digital instrument drive is achieved, the efficiency of taking NO<x> out of engine exhaust reaches 85%, the vehicle diesel engine reaches the national V emission standard, and the OBD function is achieved.