Abstract: The uncertainty and variability of requirements always affect on software life cycle，and are important factors in puzzle efficiency and quality of software development.According to the research on dynamical systems and software of complexity theory，an evolutionary model is developed，which can guide the evolution course of the software requirements and evaluate the quality of the requirements course.It shows that the evolution process of the requirements can be regarded as the normal when the consistent of requirements evolutionary process change chart and the model trajectory.The efficient and effective of this model on estimate requirements evolutionary process is illustrated by a specific example.

摘要： 需求的不确定性和易变性一直是影响软件生命周期，困扰软件开发效率和开发质量的重要因素。通过对动力系统和软件复杂性理论的研究，提出了一种混沌演化模型，该模型可以对软件需求的演化过程进行指导，同时也可以评价需求过程的质量。研究表明，只要需求演化过程的变化图和模型的轨迹图一致，那么需求的演化过程就可以看成是正常的。通过对具体实例的分析，进一步说明了该模型在评价需求演化过程上是有效可行的。