Global economic development and environmental protection requirements are increasing the demand for renewable energy rapidly. Wave energy converters are a hotspot in research, and many designs have been proposed. Pendulum-based wave energy converters, because of their sealed structure and high reliability, are drawing researchers' attention. This article considers the concept of a Vertical Axis Parametric Pendulum Wave Energy Converter (VAPPWEC) and focuses mainly on the characteristics of the pendulum system. The dynamic function of the pendulum is proposed. A new evaluation indicator, Cumulative Frequency curves of Angular Velocity (CFAV) is introduced to analyze pendulum motion accurately and evaluate the harvesting performance conveniently. The model test shows the parametric resonance zone of the pendulum with a notable boundary and the pendulum's stability under power take-off (PTO) damping. Additionally, a large-range analysis method based on the Prescribed Excitation Model (PEM) is proposed, and the output power is assessed. Linear damping performs better than constant damping, with a maximum capture width ratio of 39.05%.