A LED optical lens and an illumination device thereof are revealed. The optical lens includes a light-source side surface and an image side surface of the LED optical lens that both are designed respectively according to mathematical expressions of freeform surfaces such as Anamorphic formula and Toric formula Thus the optical lens has different curvatures along different axes. After light from LED emitting into the optical lens at a fixed incident angle, emergent light with different divergence angles along different axes is generated. For example, the divergence angle along the long axis is larger than that along the short axis. Therefore a uniform and near rectangular distribution pattern is formed on the target area Moreover, a plurality of optical lenses aligned along the same axes is arranged at a holder to form a lens array. The lens array is used together with a LED array so as to form a LED illumination device.