When the THz optical parameters of gas or liquid samples in quartz glass container were measured in the most cases, the influence of THz optical parameters quartz glass should be considered. The time domain spectroscopy of quartz glass was measured, then it′s the refractive index and absorption coefficient in THz band were calculated by the analytical formula. At last the error of its optical parameters was analyzed by the theory of error propagation. It is found that the error of the refractive index is almost invariable in 0.2-2.0 THz, and the error of the absorption coefficient is exponentially increasing with frequency increasing. The result is significant for improving the accuracy of THz optical parameters of gas or liquid samples in quartz glass container.