This invention provides a method for photocatalytic treatment of wastewater and system thereof. The method described herein is carried out in a reactor comprising: a light source; a solid rod having spaced thread profile that swirls helically along the rod, in which the rod is substantially wholly coated with photocatalyst; and a cylindrical sleeve coaxially enclosing the rod so that wastewater flows helically in the space between the thread along the rod while contacting the photocatalyst coating thereon, such that organic compounds in the wastewater undergo photocatalytic degradation upon exposure to the light source.