The beam propagation properties of the high-powered Multi-Quantum-Well (MQW) laser diode (LD) are definitive elements in many application fields such as micro-processing, biomedical technique, and basic research, etc. In this study, the beam characteristics of a high-powered InGaAs/AlGaAs MQW-LD have been evaluated in both fast-axis and slow-axis. The multi-planar waveguide model and the non-paraxial second-order moment theory were used in analyses of the beam propagation features in the direction perpendicular to the active layer of a MQW-LD. The experimental results of the beam character measurement accord with those of the theoretical calculation very well for a sampled InGaAs/AlGaAs MQW-LD. The analysis approach is thought to be useful for design of the LDs and the other waveguiding optical devices.