Abstract: The developing process of nonlinear baroclinic disturbances and the formation of fronts in pure basic baroclinic currents with uniform potential vorticity are discussed by using a three-dimensional semigeostrophic model. The results show that the development of waves depends on both the initial disturbances and on the vertical shear of the flow, the growth of waves increases with increasing vertical shear. The growth rate of waves is different for the different flow, and for a given flow. the behaviour of waves is determined by the initial disturbances. With developing waves, the great wind speed and temperature gradient occur, and the fronts are formed.