In order to solve the water leaking problem in tunnel, the unsteady thermal stress field simulation and effect of restraint conditions on early concrete of tunnel secondary lining are studied by software MIDASGEN. The study results show that: 1) The distribution of early thermal stress of the tunnel can be changed by restraint conditions. 2) The maximum tension stress filed locates in middle of tunnel secondary lining with outer restraint force; while the maximum tension stress filed locates out of tunnel secondary lining without restraint. 3) The tension stress of outer region of tunnel can be reduced by restraint; the tension stress of region away from restrained area largens; while the tension stress distribution of tunnel without restraint is opposite to that of tunnel with restraint. According to the characteristics of thermal stress distribution, the reinforcement in the middle and outer of secondary lining should be strengthened moderately in design procedure, and the restraint between primary support and secondary lining should be reduced to avoid cracks.