Sampled?data control is a major technology in contemporary control engineering,with a number of advantages such as easy modification of the control law,high reliability,good real?time performance and strong robustness against disturbance, and so on. This paper studies a controlled inverted pendulum with a sampled?data PD feedback,which is described by a differential equation with a time?variant delay,where the delay is piecewise linear with respect to time. The motion equation of the closed?loop is firstly converted into a difference equation, the effect of the delay value and the sampling period on the stable region in the gain plan is discussed, and then a method is given for calculating the optimal feedback gains that minimize the maximal module of the characteristic roots of the difference equation within the stable region. Finally, the influence of the delay and the sampling period on the convergent speed of the difference equation is analyzed. The numerical results show that both the delay and the sampling period have significant influence on the stability and convergent speed of the controlled inverted pendulum.