A color registration method of an image forming apparatus which comprises a registration sensor, the color registration method comprising: determining whether color registration is needed or not; if color registration is needed, setting an optimal amount of light of the registration sensor in a feedback manner; forming a predetermined mark for color registration correction on an image forming medium; and performing color registration correction with respect to the formed mark using the set optimal amount of light; wherein the feedback manner adjusts an amount of light of the registration sensor such that a sensed amount of light is adjusted to a predetermined target amount of light; wherein the setting the optimal amount of light is performed while rotating the image forming medium and is characterised by comprising: providing a predetermined initial control signal to the registration sensor; sensing an amount of light reflected from the image forming medium; calculating a control signal according to a difference between the sensed amount of light and a predetermined target amount of light; determining whether an amount of light of the registration sensor has a stable value or not, by comparing the sensed amount of light and the target amount of light; if the amount of light of the registration sensor has the stable value, selecting an amount of light of the registration sensor corresponding to the sensed amount of light as the optimal amount of light; and providing the calculated control signal to the registration sensor. determining whether color registration is needed or not; if color registration is needed, setting an optimal amount of light of the registration sensor in a feedback manner; forming a predetermined mark for color registration correction on an image forming medium; and performing color registration correction with respect to the formed mark using the set optimal amount of light; wherein the feedback manner adjusts an amount of light of the registration sensor such that a sensed amount of light is adjusted to a predetermined target amount of light; wherein the setting the optimal amount of light is performed while rotating the image forming medium and is characterised by comprising: providing a predetermined initial control signal to the registration sensor; sensing an amount of light reflected from the image forming medium; calculating a control signal according to a difference between the sensed amount of light and a predetermined target amount of light; determining whether an amount of light of the registration sensor has a stable value or not, by comparing the sensed amount of light and the target amount of light; if the amount of light of the registration sensor has the stable value, selecting an amount of light of the registration sensor corresponding to the sensed amount of light as the optimal amount of light; and providing the calculated control signal to the registration sensor. providing a predetermined initial control signal to the registration sensor; sensing an amount of light reflected from the image forming medium; calculating a control signal according to a difference between the sensed amount of light and a predetermined target amount of light; determining whether an amount of light of the registration sensor has a stable value or not, by comparing the sensed amount of light and the target amount of light; if the amount of light of the registration sensor has the stable value, selecting an amount of light of the registration sensor corresponding to the sensed amount of light as the optimal amount of light; and providing the calculated control signal to the registration sensor.