This paper describes the development of an opto-physiological model of a finger in conjunction with a ring-type photoplethysmography device (the Ring Sensor). This model is a combination of an optical model, a mechanical model, a skin capillary model and the arterial wall dynamics. It describes the photoplethysmographic effects due to the relative displacement and rotation of a finger to a ring-type opto-electric device that monitors the arterial pulsation noninvasively and continuously. Numerical simulations and experiments were conducted to verify and evaluate this model. This model can be used for optimizing design parameters of the ring device to obtain optimal pulse signals and to minimize the influence of noise caused by the displacement of the finger.