The automatic voltage control（AVC） system is an important tool for improving the voltage management level， reducing network loss， and ensuring secure and stable operation of power system. To resolve the problem of great voltage fluctuation due to changes of the grid connection manner， a new adaptive variable step voltage control method based on the Boltzmann probability distribution formula is proposed， in which a fast approaching method is adopted according to the difference between the target and actual voltage to perform voltage regulation function. Simulation results show that with the proposed control method， the voltage is smooth and stable， the voltage error can be corrected to some extent， and the voltage fluctuation due to system impedance changes can be effectively prevented， thus avoiding the damage to the power equipment and improving the system's voltage stability level.