A scroll air motor, also known as a scroll expander, is a relatively new concept to pneumatic actuators. In recent years, scroll air motors have been adopted by combined heat and power boilers, uninterrupted power supply, and some other energy storage systems as a new mechatronic device for energy conversion. The paper aims to develop a complete mathematical model of the scroll air motor for dynamic characteristic and energy efficiency analysis. In Part I of the paper, the geometry description of the scroll air motor is presented and the scroll driving torque is derived. In this, Part II, the mathematical model for the scroll dynamic process is described and verified by comparing the simulated and measured results. Then, the initial analysis of scroll energy efficiency is given, which explains the scroll's high ability in energy conversion.