By using the information-theoretic Wehrl entropy,the Wehrl entropy of a harmonic oscillator is obtained in thermal field.The mesoscopic RLC electric circuit is quantized.The relation between the Wehrl entropy and the quantum effects of mesoscopic RLC electric circuit is researched in thermal field.These results show that the Wehrl entropy is related to not only the engenfrequency,but also the temperature.And the quantum fluctuation and the corresponding uncertainty relation of charge and magnetic flux grow with the Wehrl entropy increasing and become small with the Wehrl entropy decreasing.So the Wehrl entropy can be regarded as a best measurement of the quantum fluctuation and the corresponding uncertainty of mesoscopic RLC electric circuit.