The application and accuracy of improvement of electrical field tunable liquid crystal filter is difficult because the pitch and spontaneous polarization of ferroelectric liquid crystals are sensitive to temperature where the molecular direction is changed by electric field. Based on the changing relation of pitch and spontaneous polarization of ferroelectric liquid crystal vs the temperature,the effect of temperature on birefringence of ferroelectric liquid crystal was discussed,the approximate formula of the transmission rate of ferroelectric liquid crystal electrically tunable filter properties according to the temperature was obtained. The effect of temperature on ferroelectric liquid crystal electrically tunable filter was numerically calculated.The results show that the transmission rate and band width increase and transmission peak wavelength moves to short wavelength as temperature increase,the effect of temperature changing on electrically tunable filter of ferroelectric liquid crystal is less than that of electrical field changing.