In the early construction period of lining concrete for the diversion tunnel of Xiluodu Hydropower Station, some cracks were found in the lining concrete. In view of this, ANSYS was employed to simulate the temperature and thermal stress of lining concrete based on the principle of elastic creep thermal stress calculation. According to the calculation result, the main causes of cracks were analyzed as follows large hydration heat and quick temperature decrease, improper surface curing measure, low temperature in the tunnel in winter, and strong restrain of surrounding rock. Moreover, measures of temperature control and crack prevention were proposed as follows to adjust concrete’s design age and optimize concrete mix ratio; to immediately spray water for concrete curing; to properly determine concrete grouting blocks; to seal the hole for thermal insulation in winter, etc. These measures were applied in the later stage of concrete construction and has effectively prevented further cracks.