提出了一种适用于机械系统的通用拓扑模型——环基树拓扑结构模型 ,研究了环基树的性质及自动生成算法 ,介绍了运动和力的拓扑表等概念 ,给出了两个基于环基树结构的通用自由度计算公式。研究结果为机械系统的计算机表达、管理、维护和加工提供了统一机制 ,构成了机械系统计算机辅助装配和性能分析统一建模的重要基础 A universal topology model for mechanical system - ring topology tree topology model is proposed. The properties of ring-based tree and automatic generation algorithm are introduced. The concepts of motion and force topology table are introduced. Universal DOF Calculation Formula of Ring - Based Tree Structure. The results provide a uniform mechanism for computer system expression, management, maintenance and processing, forming an important basis for the unified modeling of computer aided assembly and performance analysis of mechanical systems