It is presented that theoretical analysis and numerical calculations for E y 00 mode of a buried linear rectangular waveguide with Kerr type nonlinear cladding.It is shown that when the modal refractive index N equals to the refractive index of core n f,the core field distribution of E y 00 mode becomes uniform,while the cladding field reduces rapidly;for Nn f,the field amplitude distributions surfaces become convex and concave respectively.It is notified that the occurrence of uniform core field in a waveguide core may perhaps have prospective application in waveguide,optic electric and photonic devices.