The p-type 4H-SiC are ideal materials of substrate for high-power electronic devices. However, p-type 4H-SiC single crystal substrates with high quality, large size and low resistance could not be produced in China due to technological constraints. In this paper, Al doped p-type 4H-SiC single crystal substrates with a diameter of 4-inch were prepared by physical vapor transport (PVT). Dislocation defects were tested by the corrosion of KOH on the substrate. The crystal quality was characterized by high resolution X-ray diffraction (HRXRD), the crystal polytype was determined by Raman spectrum scanning, and the resistivity was measured by non-contact resistivity tester, respectively. It suggest that as-prepared substrates with low overall dislocation density and total resistivity (less than 0.5 Ω·cm) are prepared, meanwhile their crystal quality are good and crystal polytype is stable. Furthermore, the energy band structure and density of states of pristine 4H-SiC and Al doped p-type 4H-SiC were calculated via the first-principles plane wave ultra-soft pseudopotential method. The results show that the gap width decreases and the Fermi level passes through the valence band after the introduction of Al, which is considered as the characteristics of a p-type semiconductor. This elaborate study pave the way for the large-scale production of the p-type 4H-SiC substrate with high quality and low resistance.