Changes of software requirement are uncontrollable. Requirement change and its chain reactions are the most influential risk factor for the project quality during any stages of software development. Automatical requirement management can minimize the negative impact of requirements change. Automaticity of requirement change management relies on formal level and degree of standardization. Based on ideas of recursion and decomposition, this paper analyzes the requirement analysis method, referred to ROB. ROB is closer to reality. ROB is easily understandable and acceptable. ROB is a requirements modeling approach based resource, organization and business. It makes an improvement on management processes and management organization, designs the storage model by formalizing the requirement as a tree. It achieves the automatical and intelligent requirement change management by modify the tree under certain rules and constraints. In practical applications, the effectiveness of our approach has been indicated with a software tool．