A pulse "flow-stretching" technique is suggested in an attempt to increase pulse width in the CO2 lasers. The conditions, characteristics and requirements of pulse flow-stretching are elucidated. Optical cavity is located on the downstream of the dis-charge region, or they may be partly overlapped. The pulse width so broadened could be just greater than the time required for the stream to cross over the discharge region. This is an upper limit of pulse stretching. The analytical solution for non-equilibrium relaxation processes without radiation is obtained. The small-signal gain characteristics is presented. By utilizing the theory given in the articles[18,19], we have calculated the power output and the efficiency. The small-signal gain is in the range of nearly a few thousandth to a few hundredth per centimeter and energy efficiency, 5-15%. Influences of gas composition and pressure on the power output and effici-ency have been considered.