In order to improve the performance, output and material quality of the large area array type-II superlattice infrared detector, the optimal molecular beam epitaxy (MBE) growth condition of the long-wave InAs/GaSb type-II superlattice on 3-in GaSb substrate was studied. Combined with reflection high-energy electron diffraction (RHEED) fringes, the effects of different deoxidation temperature and growth temperature on the quality of 3-in epitaxial wafers were studied. The surface morphology, uniformity and lattice quality of the wafers were characterized by optical microscopy, atomic force microscopy (AFM), wafer defect inspection system, white light diffractometry, high-resolution X-ray diffractometer (HRXRD)， and X-ray diffraction simulations. After optimization, the density of defects above 1 μm of the epitaxial wafer is 316 cm^-2, the roughness is 0.37 nm, the total thickness variation (TTV) is 19.6 μm, and the cut-off wavelength at 77 K is 9.98 μm. Based on the molecular beam epitaxial growth process of 2-in long-wave type-II superlattice, the changes in the growth conditions after increasing the size of the GaSb substrate were studied. This is of reference significance for the adjustment of the conditions of III-V molecular beam epitaxy process after the size is increased. It also lays the foundation for the scale, quality and productivity improvement of the antimony-based type-II superlattice infrared detector array.