The non-functional requirements are the determinants of the software quality. The satisfaction of the non-functional requirements impacts the software quality. Considering the importance of the software quality and non-functional requirements trade-off, based on production theory, elasticity of substitution and linear programming, an approach to analyzing trade-off costs for non-functional requirements is proposed and a support tool is developed. Firstly, our previous work about satisfiability analysis on non-functional requirements is improved. A new coordination method for obtaining non-functional requirements from stakeholders is presented. Then, ontology for non-functional requirements and corresponding knowledge base are constructed. The previous reasoning for the strategies is provided for decision-making of software development and evolution. Because of the ability of addressing the conflict relationships of the non-functional requirements, our method is better for the software industry. Finally, through applying the non-functional requirements trade-off costs for maintenance and evolution of the trustworthy third-party certificate authority software case, feasibility of the proposed approach is described.