By making use of thermo-field dynamics （TFD）, the quantum fluctuations of current of the mesoscopic lossless transmission line in the vacuum state, the coherent states and the squeezed states with thermal noise have been studied. Thus the dependence of the fluctuations on temperature in these states at finite temperature can be seen. It is shown that the quantum fluctuations depend on not onh- the parameters of the transmission line but also the environmental temperature T. The higher the temperature, the more quantum noise the line exhibits.