The dynamic control process in an adaptive optics (AO) system is the third important factor to affect the performances of the AO system. A numerical simulation of the dynamic control process in an AO system is carried out for the first time to complete a comprehensive numerical simulation of an AO system. By means of the numerical simulation the long-exposure Strehl ratio and other useful metrics for evaluating the performances of an AO system can be obtained. In comparison to the theoretical analyses of automatic control theory, a numerical simulation of the dynamic control process in an AO system is advantageous. The frequency response characteristics are closely related to the dynamic control performance of an AO system. The bandwidth, phase margin and gain margin which are very important parameters for experimenters can be obtained conveniently from a numerical simulation of the frequency response characteristics. A numerical simulation of the frequency response characteristics in an AO system is presented in this paper for the first time. The numerical simulation results agree with the experimental data excellently. The simulation computational results of frequency response by using composite input of multiple frequencies compare to the single-frequency simulation results very well and can be used to determine the practical parameters of bandwidth and margins. The performances of an AO system can be effectively investigated by means of a combination of a numerical simulation of frequency response characteristics with that of the dynamic control process.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.