Abstract: Taking example for Lorenz’s chaotic system，Chen’s system，Lü’s system and Rössler’s system，several crucial problems with regard to chaos are researched，such as the mechanism to form chaotic attractors，the structural characteristic of chaotic attractors and the essential reason why the motion of a chaotic system is hypersensitive to initial value and so on.It is pointed out that each chaotic system comprises leastways two nonlinear motion modes.The state of system moves from one mode to another.The essential reason to produce chaos is nonperiodic motion switch between two modes.Asynchronous switch of two state motions from adjacent different initial conditions results in sensitive dependence on initial value.

Key words: chaotic attractor, mechanism of chaos, Lorenz’s system, Chen’s system Rö, ssler’s system

摘要： 以Lorenz系统、Chen、Lü系统和Rössler系统为例，研究了混沌吸引子形成的机理、结构特征以及混沌运动对初值敏感依赖的本质原因。指出，连续非线性动力学系统要产生混沌吸引子，至少要存在两种非线性运动模态，并在两种运动模态之间进行非严格周期地转换；相邻状态在同一运动模态中运动的逐渐分离，和在不同运动模态之间的不同时（或不同幅度）转换，导致了系统运动对初值的敏感依赖，这就是混沌运动的本质。

关键词: 混沌吸引子, 混沌机理, Lorenz系统, Chen系统, Rö, ssler系统