A low-power analog/digital conversion system of an image forming apparatus and a method of detecting a system error are provided to detect an error generated when an analog/digital converter is operated, automatically restore the analog/digital converter to a normal state, and vary a clock cycle for each channel to reduce power consumption. A low-power analog/digital conversion system of an image forming apparatus includes a controller(200). The controller automatically initializes the system so as to restore the system to a normal state when an analog/digital output value transmitted through at least one channel and converted into a digital value is deviated from a predetermined reference range, an analog/digital average value sampled by a predetermined number of times for each channel is out of a predetermined reference range, or an analog/digital conversion completion signal periodically generated in response to an analog/digital conversion clock signal is not generated within a predetermined period of time.