Starting from Zakharov integral equation, two coupled fourth order nonlinear evolution equations have been derived in deep water for two gravity wave packets propagating in the same direction in the presence of wind blowing over water. On the basis of these evolution equations, the stability analysis is made for a uniform gravity wave train in the presence of another wave train having the same group velocity. Graphs are plotted for growth rate of instability against the perturbation wave number for different values of the amplitudes of two wave trains and for different values of wind velocity.