Initiative control technology based on periodic temperature excitation was used for mixing gasdynamic CO2 laser(MGDL). Through numerical simulation, influences of periodic temperature excitation on mixing characteristic of donor and assistant flows and small signal gain coefficient of mixing gasdynamic CO2 laser were studied. Investigation results indicate that compared with the case that has no periodic temperature excitation, mixing efficiency of donor and assistant flows can be enhanced and small signal gain coefficient in mixing nozzle can be improved when periodic temperature excitation with certain excitation amplitude and excitation frequency is imposed at the outlet of assistant nozzle. Excitation amplitude and excitation frequency have important effects on mixing efficiency of donor and assistant flows and small signal gain coefficient. As the excitation amplitude increases, the small signal gain coefficient first increases and then decreases. In downstream area of mixing nozzle, small signal gain coefficients under the condition of the six excitation frequencies selected by this paper are all higher than the state without periodic temperature excitation. With the increase of excitation frequency, mixing efficiency of donor and assistant flows becomes better and better; but when the excitation frequency increases up to a certain value, mixing efficiency of donor and assistant flows will not change any more.