Effect of temperature and size on the dielectric function of noble metal nanoparticles are analyzed theoretically, and the optical properties of the nano-spheres are calculated including the dispersion relation and temperature characteristics of refractive index. The results show that the real part of dielectric function of the bulk gold material or gold nanoparticles rise with increasing of temperature, but the imaginary part demonstrate different temperature characteristics. For the absorption efficiency of the Au nano-sphere,the peak value of the absorption efficiency increased with the increasing of temperature, and the temperature sensitivity of the absorption efficiency decreases with the particle size increasing at the range of 10~100 nm.