To investigate the internal self-drying effects of hydraulic concrete and high-performance concrete with different water-cement ratios, the ratios are set to be 0. 33, 0. 41, 0. 51 for hydraulic concrete and 0. 30, 0. 40, 0. 50 for high-performance concrete. The concrete specimens were sealed and the internal relatively humidity inside was monitored for three months. The test results show that the internal relative humidity for both hydraulic and high-performance concrete in the sealed state has two periods, namely the humidity saturation period and the humidity drop period. As the water-cement ratio decreases, the duration of the humidity saturation period gradually decreases. The drop rate of the relative humidity for high-performance concrete is higher than that for hydraulic concrete with the same water-cement ratio, and the duration of humidity saturation period for the former is shorter. The internal relative humidity of hydraulic concrete with the water-cement ratio 0. 5 in the sealed state does not drop substantially but with the water-cement ratio 0. 41, it drops slowly due to the self-drying effect. When the concrete dries gradually, it shrinks slowly, which provides a new idea to analyze the long-term instability mechanism for the strain with the deduction of temperature strain, called the no-stress-gauge strain in the Xiluodu ultra-high dam project.