Single-stage buck-boost gird-connected inverter is widely used in distributed generation systems because of low cost and high efficiency. However, shoot-through problem exists, so reliability of the system is reduced. In addition, output voltage of renewable energy resources varies widely with load and environmental condition, so voltage stress of switches is high in wide input-voltage range application. An improved single-stage buck-boost gird-connected inverter is proposed. It can operate at buck and boost modes, so it is suitable for wide input-voltage range application. Operating principle is illustrated. Simulation results verify the theoretical analysis of the inverter.