The power generation in a gasdynamic laser (GDL) has been theoretically studied. Quasi‐one‐dimensional unsteady flow equations are numerically solved simultaneously with the rate equation for the laser intensity inside the laser cavity. Steady‐state coupled solutions for the field variables and the laser intensity inside the GDL cavity are obtained by a time‐dependent numerical technique. The laser intensity variations along the axis of the flow (across the laser cavity) are computed for different laser gas mixture compositions and reservoir conditions. The analysis predicts a sharp spike in the laser intensity at the leading edge of the laser cavity followed by a sharp fall from which it recovers to a uniform constant value for the lower H2O concentrations. It is shown that the H2O concentration above 2% in the CO2‐N2‐H2O gas mixture is detrimental to the power generation.