IT capability is critical significant to build enterprise agility and promote organizational performance. However, IT capability is always treated as the causal factor already existing and there are few studies on how IT capability is developed. To address this research question, we choose M company, one of the largest fast growing entrepreneurial e-commerce enterprise in China, and conduct a single case study to analyze how IT capability is formed accompanying business’s fast growing. We find that M company has designed and implemented many specific mechanisms in order to tackle the problems caused by business’s fast growing. For a specific problem, what M company has done could be categorized into three periods, respectively pre-event, during-the-event and post-event. M company has obtained an agile IT capability composed of scientific planning capability, improvisation capability and timely feedback capability in the three periods individually by tackling different problems flexibly. We also summarize a process model to illustrate the approach of how IT capability is formed. Finally, the theoretical and practical implications are also discussed.