In light of the low damping and low frequency oscillation problems of AC/DC parallel power system, a coordinated damping control method of generator and gird in AC/DC parallel power system based on mixed H2/H∞ control theory is proposed. Firstly, system oscillation model and open-loop reduced order model are identified by the total least squares-estimation of signal parameters via rotational invariance techniques(TLS-ESPRIT) algorithm. Combining H2/H∞ control theory and adopting the solution method of linear matrix inequalities and the output feedback structure, the supplementary robust damping controllers of high voltage direct current(HVDC) and generator is designed, whose advantages are easy to be solved, with simple construct of controller, and having strong robustness. In the end, a four machine in two domains test system is built in PSCAD/EMTDC, and compared with the traditional additional damping controller, the simulation results verify the effectiveness and robustness of the coordinated damping control of generator and gird.