According to the self-consistent electronic dynamic transport theory of mesoscopic system, we present the dynamic conductance of mesoscopic structure. As an application of this theory, we employ a coherent mesoscopic parallel-plate capacitor model in the present study. The results show that the dynamic conductance of system depends on the frequency of external field and Fermi energy of system, and is a complex with a finite imaginary part. For a smaller frequency, the conductance shows a similar feature to dc case, but with the increase of the frequency of external fields, substantial deviations between dc case and ac case are observed, the dynamic conductance of system presents a peak structure with Fermi energy varying. For a given Fermi energy, the dynamic conductance is oscillatory with frequency varying, moreover some negative imaginary parts of conductance are observed. The negative imaginary part implies the capacitive behavior, and positive imaginary part refers to the inductive behavior.