Lifetime assessment of steam turbine components has become more and more important for the past years. Tower solar turbines experience a greater number of start-ups than those operating in base-load plants and high levels of thermal stress occurs during fast start-up, which both have a significant impact on lifetime. To achieve the fastest start-up time without reducing the lifetime of solar turbine it is essential to fully understand the thermal behavior of the turbine components during start-up. A series of experiments have been carried on a combined cycle steam turbine. The operation mode and inlet parameters of experiment unit are similar to tower solar turbine, so the new thermal model of heat transfer coefficient based on these experiment data can be used for the start-up research of tower solar turbine. A Finite Element (FE) turbine model is created and analyzed with the new thermal model in many start-up cases such as warm start, hot start to seek for an optimized start-up mode.