Based on the bidirectional fast Fourier transform beam propagation method (FFT-BPM), a self-consistent Nd:Ti:LiNbO3 Fabry-Pérot waveguide laser model has been developed. By using the bidirectional FFT-BPM and the attenuation effect of pumping and resultant lasers within the waveguide cavity, the interference effect and physical behaviors of the population inversion longitudinal and transversal spatial effects were observed. The resultant laser power is saturated if the waveguide is longer than a critical length, which is a function of the pumping power. Moreover, the resultant laser power density is a nonuniform function along the longitudinal dimension within the waveguide cavity. © 1999 American Institute of Physics.