An apparatus and a method for controlling exhaust gas purification for a diesel engine

In a cold condition before a warming-up completion in a diesel engine, when an engine power is less than a predetermined value, an air excess rate is controlled to a second air excess rate being smaller than a target air excess rate set after the warming-up completion, thereby promoting a warming-up of an exhaust gas purification catalyst due to rise of an exhaust gas temperature, and when the engine power is more than the predetermined value, the air excess rate is controlled to a first air excess rate being larger than the target air excess rate, thereby decreasing HC emission quantity from a combustion chamber. Accordingly, a total emission quantity of HC at the clod condition is decreased.