Due to many remarkable physical and chemical properties, two-dimensional (2D) nanomaterials have become a hot spot in the field of condensed matter physics. In this paper, we have studied the structural, mechanical, and electronic properties of the 2D GaInO3 system by first-principles method. We find that 2D GaInO3 can exist stably at ambient condition. Molecular dynamic simulations show that GaInO3-sheet has excellent thermal stability and is stable up to 1100 K. Electronic structural calculations show that GaInO3-sheet has a band gap of 1.56 eV, which is close to the ideal band gap of solar cell materials, demonstrating great potential in future photovoltaic application. In addition, strain effect studies show that the GaInO3-sheet structure always exhibits a direct band gap under biaxial compressive strain, and as the biaxial compressive strain increases, the band gap gradually decreases until it is converted into metal. While biaxial tensile strain can cause the 2D material to transform from a direct band gap semiconductor into an indirect band gap semiconductor, and even to metal. Our research expands the application of the GaInO3 system, which may have potential application value in electronic devices and solar energy.