The time evolution of a quantum state of mesoscopic LC circuit are studied in detail by using thermo-field dynamics （TFD） at a finite temperature. The result indicates that the quantum state of a mesoscopic LC circuit evolves from the thermal vacuum state to coherence state and go on by the action of an external impulse functional signal on the circuit;the thermal squeezing properties of charge and flux appear in the circuit under some conditions;and furthermore, the typical quantum squeezing effect may occur when certain conditions and particular temperature are meet.