It is useful that uniform electric field exists in nonlinear waveguides.Theoretical analysis and numerical results for typical examples are carried out for the condition of the uniform core field of TE 0 modes in a three layer planar waveguide with two identical Kerr type nonlinear claddings and a linear core.Electric field of core becomes uniform when modal refractive index equals the refractive index of the core or normalized modal refractive index equals 1.Formulas and curves of field distribution and total power in terms of normalized parameters are given for focusing and defocusing claddings.