Besed upon the quantization of a mesoscopic lossless transmission line, we obtain the quantum fluctuations of the current and the voltage on inductance of the unit length line in the thermal Fock state by thermal field dynamics (TFD). The dependence of the quantum fluctuations on temperature is analysed. It is shown that the quantum fluctuations depend on not only the distribution parameters of the line, the angular frequency of the signal and the photon number, but also the temperature T.