A novel switch-mode power amplifier based on a multicell multilevel circuit topology is introduced in the paper. The Cascade Multilevel Class-D Power Amplifier's topology is analyzed. Due to the phase-shifted PWM control of the individual switching cells, the output voltage ripple of the total system is considerably small. After studying the Single-phase H-bridge inverter's output with unipolar Pulse Width Modulation, the paper lays emphasis on the researching on the cascaded H-bridge multilevel inverter's output. The amplifier enjoys a switching frequency, which are 2N times of that of a single unit. It has a small total output voltage ripple and only requires a small filter to suppress the switching frequency harmonics. Then a cascaded unipolar Pulse-Width Modulation H-Bridge multilevel class-D power amplifier is built in the laboratory. The measurement result shows that the proposed amplifier has good following performance and stability.