Recent progress in numerical modeling of H- ion sources has been reviewed. The following two topics are mainly the focus: (1) the origin of the nonuniformity of H- production and H- beam in large H- sources and (2) extraction physics, especially the role of the "weak" transverse magnetic field on H- extraction. The present understanding of the origin of H- beam nonuniformity is reviewed and discussed with the results by a series of Monte Carlo transport modeling of electrons, neutrals, and H- ions. Also, the physical mechanism of the large enhancement of H- extraction due to the weak transverse magnetic field is discussed with the particle in cell modeling. In addition, some new results on the effect of surface H- production on the electric potential structure near the extraction aperture are presented and discussed.
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