Many distance education researches have pointed out that students are often forced to study in isolation due to the lack of support from mates and regular attendance. Thus, the objective of this research is to find effective group composition methods to increase the interaction among students in asynchronous distance education using the theories of cooperative learning, group dynamics and social cognitive theory as foundations. The outcome can be a reference for the design of network cooperative learning activity and web-based instructional system in the future. This study is conducted in NSYSU Cyber University using surveys and observations to investigate the influence of cognitive style on cooperative learning when different types of tasks are assigned. This research concludes that the choices of discussion tools in the chat room are different under intellective and decision-making tasks. Moreover, regardless of the task types, the heterogeneous groups outperform the homogeneous group during the cooperative learning process. Finally, the cognitive style is significantly related to group satisfaction in a cooperative learning environment