【摘要】提了基于二阶线性系统等倾线法绘制相平面原理，实现了高阶非线性控制系统相平面相轨迹的作图算法。该算法与解析法相比具有计算简单、结果精度高的特点，其作图可推广到非线性微分方程的求解。实例结果证明算法是有效的。关 键 词 相平面; 相轨迹; 等倾线; 高阶非线性In this paper a new concept of phase contrail of phase plane for higher order nonlinear control system based on isoclines method of second-order linear system is proposed. It features simplicity in calculation , higher precision in consequence compared with analytic method .It can be applied generalized to solve non-linear difference equation.The results of example show that algorithm is effective.