There are many risk items of the requirement phase that cause the defect occurring in the latter phase and the quality problems during process management and project progress. This paper designs the opportunity tree that requirement manage the defects and their problems solution as well. For the similar projects, we can estimate defects and prepare to solve them by using domain expert knowledge and the opportunity tree, which can greatly improve the software process. And this paper identifies risk items to produce reliable software and analyzes in the requirements phase. Also, this paper is intended to develop the relationship between defects and their causes to introduce. Therefore, using defect causes, we understand the associated relationship between defect triggers and design Opportunity Tree to manage the defects.