By virtue of the thermo field dynamics and the coherent thermo state representation, the Wigner function of mesoscopic RLC circuit at finite temperature was obtained, and the quantum fluctuations of mesoscopic RLC circuit at finite temperature were studied. By means of the Weyl correspondence and Wigner theorem the marginal distribution of Wigner function in mesoscopic RLC circuit was discussed. The physical meaning of marginal distributions′ statistical average of the Wigner function was explained. The results show that the quantum fluctuations of both charge and current of mesoscopic RLC circuit at finite temperature increase with the rising of temperature and resistance value, and the mesoscopic RLC circuit has squeezed effects between charge and current, caused by the quantum mechanical zero-point fluctuations; the marginal distributions′ statistical averages of the Wigner function are the energy stored in capacity and in inductance of the mesoscopic RLC circuit, respectively.