This paper researched into the delignification mechanism and the relations of black liquor lignin content and alkali concentration to pulping time under the cooking process conditions of wheat straw sodium sulfateanthraquinone( AQ) pulping with Microwave radiation. The results showed that delignification process was divided into two stages: quick stage and slow stage. The lignin removal rate in the first stage was much higher than the second stage, that is, lignin has been removed more sufficiently after quick stage. In this stage, reaction order of delignification was 1.5, and 0.5 with respect to OH-, the activation energy was 51.90 kJ • mol-1. The latter delignification belonged to the first-order reaction and 0.3 with respect to OH-, the activation energy was 72.20 kJ • mol-1KJ. Apparently, slow stage needed to consume large amounts of energy to removal lignin.