This paper proposes a cognitive model to classify the level of cognition and cognitive activities in program comprehension. This model is composed of input, cognitive process and output, among which the cognitive process includes four activities (absorption, denial, reorganization and expulsion) at six Bloom learning levels. Compared with the existing models, our learning model is more complete and more detailed. It not only describes cognitive activities in detail, but can also be applied in most of the cases. Our model can also reveal the differences between experts and novices in program comprehension. It provides some useful insights on how to build a tool to aid program comprehension. We also find that the so called traditional program comprehension process involves activities not only at comprehension level of the Bloom?s taxonomy, but at higher levels as well. A case study is conducted to validate this learning model.