Abstract: In the underwater source localization of matched-field processing (MFP), the accuracy and efficiency of the replica model for the field prediction is of the essence. Especially in deep ocean, those models usually used in shallow water can not have an satisfying efficiency. The ray theory based Gaussian beam method, with merits of high efficiency, clarity in physical meaning, and being easy to be paralleled, is proposed for sound field prediction. Simulations and experiment data processing are performed to validate this method. The results indicate that the application of Gaussian beam model as a replica model in deep water localization has high accuracy.