Shrinkage stress of cementitious materials will generate if the dry shrinkage is restrained in drought condition. Shrinkage stress has influence on crack resistance of cementitious materials. The dry shrinkage of cementitious materials in different relative humidity was studied with Climate Simulation System. The dry shrinkage change law of concrete in 20°C, 60% relative humidity for 500 days and in 20°C, 10% relative humidity for 180 days was compared. The relation between water loss rate and shrinkage rate of cementitious materials in drought condition was analyzed.