An operation method of an optical touch system is provided. The imaging lens includes a first lens having positive power, a second lens having negative power, and a third lens having positive power and an inflection point on an imaging surface thereof facing an image side, wherein the first to third lenses are sequentially arranged from an object, and the second lens has power stronger than power of the first and third lenses. The laser beam passes through a distributive lens focusing assembly and to the Kerr material.