In this paper the author investigated the vertical distribution of vertical velocity, by applying the double-Fourier series to the c-equation. And we can derive the conclusion that the parabolic distribution usually assumed in the parametric representation does hold generally in the large scale disturbances, but its validity is questionable for the small scale disturbances. It may be said that the level of the maximum vertical velocity locates at the 500 mb level for the large scale and at the 700 mb level for the small scale disturbances, and such displacement depends upon the stability of the atmosphere.