A heat transfer analysis during the curing process in UV-Nanoimprint lithography was carried out. To imprint nano/micro patterns into a large-area target glass such as LCD panels, a mold with a poly-urethane-acrylate layer is often used, on which layer the micro/nano patterns are inscribed for the UV-NIL process. After UV resin is coated between the target glass and the flexible mold, the UV resin is cured by exposing UV light on the resin. In the curing process, heat from the phase change of the resin and the radiation by UV lamp would induce a temperature change and thermal distortion of the mold. In this study, we measured the temperature change of the flexible mold, and established an analytic model of the heat transfer. From the result, we derived the thermal properties of the PUA layer, and a thermal resistance layer between the PUA and the cured resin layer.