Unveiling the microstructural and electronic properties of β-Ga2O3 on different substrates is vital to realize the high quality and performance of β-Ga2O3. Here, the microstructure disorder, defect characters and orbital structures of β-Ga2O3 on the Al2O3, MgO, and SiC substrates with different terminations are studied. Although several growth mechanisms for β-Ga2O3 are observed on the same substrate, β-Ga2O3 prefers to deposit the octahedral Ga atom firstly on the Al2O3 and MgO substrates, and the latter can restrain the oxygen-vacancy formation and migration. The structural disorder, band offsets and gap states can be improved upon depositing β-Ga2O3 on a substrate with metal terminations under the oxygen-poor conditions. Compared to the Al2O3 substrate, β-Ga2O3 on the SiC substrate shows a smaller structure disorder and a higher defect formation energy, in particular under the oxygen-rich conditions, since β-Ga2O3 prefers to deposit the tetrahedral Ga atom firstly on the SiC substrate to form a SiC-Ga2O3 interface with less dangling bonds. The type-II band alignment of the SiC-Ga2O3 interface can be changed into the type-I character with larger band offsets when β-Ga2O3 is deposited under the oxygen-rich conditions, irrespective of the termination of the SiC substrate. These results provide a useful understanding of the effect of substrates on the quality and performance of β-Ga2O3 and a scientific basis for the application of substrate-Ga2O3 interfaces.