Abstract: A formula of ponderomotive force of whistler waves has been derived in this paper.It shows that when the wave frequency ω<Ω_e/2 (Ω_e: the gyro-frequency of the electrons),the electrons intend to move into the region where the wave amplitude is larger.As a result,a density crest is formed along the propagation path of the wave.When ω>Ω_e/2,the situation is just reversed,the ponderomotive force intends to sweep out the electrons from the region where the wave field is more intense,resulting in formation of a density through along the propagation path of the wave.Therefore,the Weibel's results are just the special case (ω<<Ω_e) of the results presented here.