Abstract: Based on the general theoretical model of multibeam laser-plasma instabilities (LPI), we derived the LPI dispersion relation applicable to arbitrary beam configurations, polarizations, and wavelengths, and developed a multibeam LPI dispersion relation program. We applied the theoretical model to the SG-100kJ facility and the SG-Octopus experiment, qualitatively explaining the observed “intra-cone asymmetry” and “each-beam-goes-home” phenomena. Numerical simulation results indicate that multibeam effects exist in both phenomena and may be one of the important factors affecting the development of instability. The development of this model and program provides a tool for the prediction and control of multibeam instabilities in laser fusion facilities.