A controlling system and method for controlling an electrochromic element, utilizes a simplified architecture, including at least a microcontroller, a A/D converter and a charging circuit, to reduce complexity of the whole system for reaching both of a respond time and cost savings for the electrochromic element. And the controlling system and method only utilizes a fixed frequency to drive the electrochromic element for reaching a better reliability than a variable duty cycle driver used in prior art.