An infrared ray tracking lens is adapted to receive light from a target object, including a first positive refractive lens, a second positive refractive lens, a negative refractive lens and an imaging unit. The first positive refractive lens includes a first lens surface which is a convex surface and a second lens surface which is a concave surface. The second positive refractive lens includes a third lens surface and a fourth lens surface, wherein the third lens surface is a convex surface. The negative refractive lens includes a fifth lens surface and a sixth lens surface, and the fifth lens surface is a concave surface. The first positive refractive lens, the second positive refractive lens and the negative refractive lens are arranged along an optical axis, wherein the first, third and fifth lens surfaces are oriented towards the target object, and the second, fourth, and sixth lens surfaces are oriented towards the imaging unit.