In this paper, an off-grid power inverter for the application of the photovoltaic (PV) power-generation system is proposed. The PV power-generation system used by an inverter supplies a utility sinusoidal source. To obtain the maximum power of the PV power-generation system and the low total harmonic distortion of the off-grid power inverter, a linear approximation control algorithm method and a sinusoidal pulse width modulation (SPWM) method are adopted. On the basis of an advanced control technology to obtain the optimum dynamic regulations of the off-grid power inverter, a peripheral interface controller and a SPWM microcontroller are used. Finally, to verify its feasibility, a prototype of the off-grid power inverter is built. Theoretical and experimental results are presented to demonstrate the performance of the off-grid inverter.