1. An interaction control system, comprising: a light source module, projecting a pattern to a detection region, wherein the pattern has a plurality of parallel lines extending toward a predetermining direction; an image capturing device, capturing images of the detection region and generating an image information stream based on the images; and a processor, coupled to the image capturing device for obtaining a subtracted image information by subtracting the currently captured image information to a background image information of the detection region so as to determine whether or not an object appearing in the detection region, when the object appears in the detection region, calculating a motion of the object based on a variation of the pattern imaged on a surface of the object toward the light source module, and generating corresponding control instruction to a host apparatus, wherein the processor detects variation of line width of the surface of the object according to amount of pixels having the absolute value of the gray scale greater than a predetermined value, and the processor determines that the object is closer to a reference point when the line width of each line imaged on the surface is thicker and determines that the object has a farther distance from the reference point when the line width of each line imaged on the surface is thinner.