Commonly used methods for design and analysis of a rod pumping installation assumed a vertical well and ignored the well curvature effect, rod/tubing drag forces and fluid dynamics. These methods could cause substantial errors if they are used to diagnose and analyze the rod pumping system in the deviated wells. This paper presents a new and simplified model to design and evaluate the performance of rod pumping system. Using a 3D quasi-static model involving all the equilibrium equations and deflection equations, the rod loads displacements and stresses for each element are solved recursively. The lateral displacement of the rod is also considered in the model. The possible contact between the rod and tubing is estimated if the rod is supported at certain places, for example, where a centralizer is placed. Taking into account the well geometry, the rod centralizer effect, the fluid viscous effect, the Coulomb friction between rod and tubing, and all the components in the system, the model provides a useful and simple method to design the rod strings and spacing of the rod centralizers, to select the pumping mode for optimization of the system, and to evaluate the performance of a existing pumping system. An efficient computer code is developed. Finally, good agreement is indicated between the results and the actual measured data.