An optical lens including a lens barrel, a fixing ring, and at least one lens element is provided. A bonding surface is provided on an inner side of a periphery of an end of the lens barrel, and a plurality of micro-structures are disposed on the bonding surface in a ring-shaped arrangement. The micro-structures protrude from the bonding surface. The fixing ring is disposed inside the bonding surface of the lens barrel. The lens element is disposed inside the lens barrel. The micro-structures on the bonding surface and the fixing ring are dissolved by a solvent, so as to fix the lens element inside the lens barrel. An assembling method of the optical lens and a lens barrel are also provided.