Based on the occurrence conditions of Hopf bifurcation of a delay system and corresponding handling methods, we have proposed an analytic method for achieving the controlling conditions when a low-dimensional chaotic system is controlled by applying time-delayed feedback on a control variable. Using an analytic method, we can obtain the functional relation of various parameters at the critical points. This method has been applied to some examples and the results show that it is an important means to control chaotic systems.