In the past, any Electro-Static Precipitator ESP) control by means of conventional control methods was not optimal control. In this paper, the authors analyse ESP dynamic characteristic and formulate state space equations and discuss new control strategies by modern control theory, the authors take silicon controlled rectifier (SCR)regulation voltage circuit as a controlled member which includes SCR, ESP electric field, sampling filter circuit etc. the paper assume that the relationship between SCR conduction angle and the effective value of its output voltage is approximately linear, and that magnetizing current and current- limiting resistance are very small. The controllability of the controlled member is analysed, the pole assignment of the control system is discussed, and the stability condition of the feedback control system is given. The paper also discusses the optimal control of ESP, and presents its objective function, boundary conditions and solution of the control. The result shows that modern control of ESP is easily realized by computer and the effect of ESP control is satisfactory.