With respect to the stable control of horizontal-track,straight-line inverted pendulum,with the help pf harmonic control method based on non-linear system extension theorem,the paper realizes the control of the trolley's level position and the swing link's vertical position.Compared with the other methods,this method does not need the linearization of nonlinear systems,and imparts more realness to system models.The simulation experiment indicates that using this method,a more manipulative effect can be achi...