The variation behavior of phase retardation of wave-plate with temperature was introduced, and the electro-optic modulation method was put forward to measure the phase retardation. The variation of temperature has an effect on the phase retardation, thus influencing the useful precision of wave-plate. In order to reduce this negative effect and improve the precision under different temperature conditions, the properties of the wave-plate should be analyzed. The temperature properties were analyzed theoretically and mathematically, then relationship between coefficient of thermal expansion and temperature coefficient of refractive index was obtained. The relationship between temperature coefficient of refractive index and wavelength offered theoretical basis and parameter choice basis for correctly using and designing wave-plate, respectively. The retardation would reduce 1° when the temperature increased 1 ℃ for the wave-plate with thickness of 1.8 mm and wavelength of 632.8 nm. According to the application shortage of wave-plate in different temperatures, the electro-optic modulation method was presented to measure the phase retardation, if the voltage was controlled within the range of ±700 V, the precision of measuring would be within 1%.