The calculation of the temperature-dependent dielectric function of metal is modified. A method to control the reflection index of mirror by using the surface plasmon resonance (SPR) is proposed. A polymer film with high thermooptic coefficient is coated on the metal film in the Kretschmann configuration. The variations of metal film thickness and dielectric constants for all layers with temperature are calculated, and the proposed device is numerically simulated by using the characteristic matrix method. The results show that when the incident wavelength is 532 nm, the temperature is controlled between 10 ℃ and 90 ℃, the reflection index can be controlled from 52.8% to 41.5% for 70° incident angle and 31.1% to 18.8% for 75° incident angle, respectively.