In this paper,we consider the modified one-dimensional Schr?din-ger equation:(Dt-F(D))u=λ|u|2u,where F(ζ)is a second order constant coefficients classical elliptic symbol,and with smooth initial datum of size ε(<<)1.We prove that the solution is global-in-time,combining the vector fields method and a semiclassical analysis method introduced by Delort.Moreover,we get a one term asymptotic expansion for u when t →+∞.