By use of material studio software, the lattice constant, band energy gap and optical permittivity of silica are calculated, and to be used as the key parameters to investigate the microwave dielectric properties of silica.It is found that its permittivity and loss are increased with increasing temperature.In addition, the ionic conduction loss caused by the defects in silica is very small from the calculation and the value is about 10-5 level at 2000K.It is found that the result of the phenomenological analysis of the dielectric properties is consistent with the experimental data.The application of this analysis allows estimate the permittivity and dielectric loss of silica both at high temperature and microwave band, which is currently still difficult to be measured directly.