Soil salinity and sodicity severely degrade soil structure and hydraulic properties in arid regions, limiting agricultural productivity. This study investigated the effects of reduced fertilizer combined with humic acid (HA) and biochar (BC) on the physical properties of sodic soil. A three-year field experiment included five treatments: an untreated control (CK), full fertilizer application (F, 700 kg/ha compound fertilizer with 1:1:1 NPK ratio), reduced fertilizer combined with HA (FA, 350 kg/ha fertilizer + 3000 kg/ha HA), reduced fertilizer combined with BC (FB, 350 kg/ha fertilizer + 3000 kg/ha BC), and reduced fertilizer combined with both HA and BC (FAB, same rates). Results demonstrated that the FAB treatment synergistically enhanced soil aggregation, increasing the content of >2 mm macroaggregates by 7.10-fold in the surface layer and improving aggregate stability (mean weight diameter increased by 2.62-fold) compared to CK. It also reduced soil bulk density by 17% and increased saturated water-holding capacity by 47%. Strong correlations indicated that aggregate stability governed improvements in porosity and water retention. These findings provide a mechanistic basis for using combined organic amendments with reduced fertilizer to rehabilitate sodic soils in terms of soil structure and hydraulic properties.