A thermochromic substrate and a pair-glass with a thermochromic thin film, which increases the efficiency with which solar energy is transmitted and blocked. The thermochromic substrate includes a base substrate, a thermochromic thin film coating the base substrate, and a high-refractivity thin film coating the thermochromic thin film. The high-refractivity thin film shifts the reference wavelength in the infrared range, at which the variance in the transmittance due to the phase transition does not exceed 0, to a shorter wavelength. The efficiency with which solar energy is transmitted and blocked is increased, thereby decreasing the load of cooling and heating a building.