Based on first-principles calculation method, the electronic structure and magnetic interactions of Ti-doped β-Ga2O3 and Ti-VO-co-doped in β-Ga2O3 have been investigated. The calculated results indicate that Ti atom tends to substitute the Ga atom at the octahedral coordinated site and the doped system prefers spin-polarized state. The magnetic moment of Ti-doped β-Ga2O3 is 0.546 μ B per cell, which mainly arises from Ti 0.48 μ B. The origin of ferromagnetism in Ti-doped β-Ga2O3 can be explained by a double-exchange mechanism. When a VO defect is introduced into Ti-doped β-Ga2O3, the magnetic moment increases and the ferromagnetic coupling between Ti atoms is strengthened. The influence of VO defect on ferromagnetic properties of Ti-doped β-Ga2O3 comes from the enhancement of hybridization between Ti-3d and O-2p states.