In this paper, we suggest that the flight broadening should be an important factor governing line profile in a high-speed gas laser with inhomogeneously broadened line, if the characteristic flow time τj is comparable to the collision relaxation time τc. The integration -representation of profile was deduced. The width of line increases inversely proportional to t, i.e., under the proxi- mate condition of effective line width, where t=τj/τc, is the flowing parameter.