It has been found that the optical bistability and multi-stability of CO2 laser can be realized when an electro-optical modulator is inserted into thecavity of the laser to change the Q-value of the laser by opto-electric signal proportional to output intensity of the laser. The mathematic model for the laser has been set up which is described by three nonlinear first-order differential equations. Its steady state model shows the characteristics of bistability and multi-stability which is confirmed by theoretical analysis and numerical calculation.