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.