Abstract: A beam-column theory is proposed forbent housing positive displacement motor (PDM) assemblies with medium-shortradius (K=1^\circ/m \sim 3^\circ/m) of building capability.According to the conditions of continuity at thesupport and the boundary of the bottom hole assembly (BHA), the mechanical modelsof PDM building assemblies in horizontal wellsof medium-short radius areestablished based on the non-uniform stiffness beam-column theory and theapplication of equivalent load to beam-column with initial bent angles.Furthermore, the side force of the drill bit can be caculated and is used topredict the building capability of bent housing PDM assemblies.%This method can be used for bent housing PDM design and well-path control.