P-type nanostructured α-MgAgSb by virtue of its intrinsically low thermal conductivity and environment friendly characteristics has drawn a great deal of attention for low temperature power generation. In this study, MgAgSb alloys were successfully prepared via ordinary planetary ball milling, followed by a spark plasma sintering process. In addition, we explored the effects of phase composition and micro-pores that can be rationally engineered via simply controlling the spark plasma sintering pressure on the thermoelectric performance of MgAgSb alloys. The results show that the carrier mobility is significantly increased from 55.1 cm² V⁻¹ s⁻¹ for MgAg_0.95Sb_0.99 with a sintering pressure of 20 MPa to 87.7 cm² V⁻¹ s⁻¹ for ones with a sintering pressure of 80 MPa due to the increase of crystallinity and the reduction of pore size, resulting in a high power factor of 2214.0 μW m⁻¹ K⁻². Simultaneously, a large number of micro-pores can strengthen the phonon scattering to reduce the lattice thermal conductivity. As a result, a peak ZT ∼1.22 at 473 K and a high average ZT ∼1.11 from 323 K to 573 K were achieved for the sample MgAg_0.95Sb_0.99, which was synthesized under a sintering pressure of 80 MPa. This work reveals that the thermoelectric performance of MgAgSb alloys can be enhanced via controlling the pore effect, which could provide guidance for the synthesis and optimization performance of other thermoelectric materials.