Lens temperature is a dominant factor for lens performance in steppers. The lens temperature of steppers was controlled tightly with TCU system. This paper aims to discuss lens UDOF, NCE, Astigmatism, FPD, IPT, lens heating performance and CD repeatability. From experiment result, the optimized lens temperature is 22 degrees C of '74' lens. It resulted in maximum UDOF, minimum Astigmatism, minimum FPD, minimum NCE and minimum IPT. And under this temperature, there is minimum Intra-field CED STD and range on the conditions of lens cooling and heating. Non-optimized lens temperature will result in UDOF decrease and Aerial image distortion.