The physical and mathematical models of CO2 laser with feedback control of detuning has been set up. The analysis of steady state shows that the optical Disability between the pump rate and the output intensity of the laser will appear when the feedback coefficient exceeds the critical value. Eesults of linearized stability analysis indicate that the necessary condition of the dynamical instability is that the Debye-relaxation rate of the detuning (bandwith of the feedback circuit) must exceed the decay rate of the population invergion. The instability appears only when the laser pump falls into a proper region. The behaviours of the period-doubling "bifnroation and chaos have been pfbved by the result of numerical calculation. The frequency of the Hopf bifurcation predicated by the stability analysis is oonaiatent with that given by the nnmerioal calculation.