Abstract: The evolution character of a isolated wave-packet produced by a point source in threedimensional boundary layer on a swept flat plate is investigated. From numerical solution of lineareigenvalue problem of spatial mode, the amplitude and phase of wave-packet at each position onthe growing path is obtained from the integral over all spanwise wavenumbers of colltribution toit's amplitude. The steepest descent method is also used to evaluate it's asymptotic behavior. Itis demonstrated that the streaks observed...