A projection system and a control method of a driving current thereof are provided. A power supply of an illumination module provides the driving current to drive a light source to provide an illumination beam. A filter wheel receives the illumination beam and filtered beams are generated. The illumination beam passes through the filter wheel during a first period and a first filtered beam is generated. The illumination beam passes through the filter wheel during a second period and a second filtered beam is generated. The filtered beams include the first filtered beam, the second filtered beam, and an intermediate filtered beam generated during an intermediate period between the first and second periods. A control device controls the power supply to continuously provide the driving current from the first period, through the intermediate period, to the second period.