Formulas and method of calculation are presented for analysis of optical nonlinearity and bistability of TE modes in a multiple quantum well waveguide with nonlinear cladding. It is demonstrated that in the thin film approximation, the method of root-mean-square equivalent index for the waveguide core is an accurate, efficient and time saving method for characteristics analysis. Dependence of modal refractive index on total waveguide power, bistability between core power and total power, dependence of field profile on modal index are analysed and the influence of waveguide parameters on them are discussed.