Abstract: In recent years through in-situ electric field measurements in interplanetary space the local nonlinear ion electrostatic waves are often identified. They may be directely related to the acceleration of the auroral particles. These electrostatic waves are considered as either the ion acoustic mode evolution or the ion cyclotron mode evolution. In this paper the evolution of the ion nonlinear waves with small amplitude for oblique propagation in the magnetic fields are studied and the nonlinear Schrodinger equation is obtained. Calculation results show that it is possible for both the ion acoustic and the ion cyclotron solitary waves to exist. After making a comparison of the results with the electric field measurements on board of satellite S3₃ some observations can be well explained.