The nonlinear stability problem in nonparallel boundary layer flow for twodimensional disturbances was studied by using a newly presented method called Parabolic Stability Equations (PSE). A series of new modes generated by the nonlinear interaction of disturbance waves were tabulately analyzed, and the Mean Flow Distortion (MFD) was numerically given. The computational techniques developed, including the higherorder spectral method and the more effective algebraic mapping, increased greatly the numerical accuracy and the rate of convergence. With the predictorcorrector approach in the marching procedure, the normalization condition was satisfied, and the stability of numerical calculation could be ensured. With different initial amplitudes, the nonlinear stability of disturbance wave was studied. The results of examples show good agreement with the data given by the DNS using the full NavierStokes equations. The nonlinear stability problem in nonparallel boundary layer flow for twodimensional disturbances was studied by using a newly presented method called Parabolic Stability Equations (PSE). A series of new modes generated by the nonlinear interaction of disturbance waves were tabulatedly analyzed, and the Mean Flow Distortion The computational technique developed, including the higherorder spectral method and the more effective algebraic mapping, increased greatly numerical and rate of convergence. With the predictorcorrector approach in the marching procedure, the normalization condition was satisfied, and the stability of numerical calculation could be ensured. With different initial amplitudes, the nonlinear stability of disturbance waves was studied. The results of examples show good agreement with the data given by the DNS using the full NavierStokes equations.