The tooth face width characteristics of offset face-gear drive are considered in this paper. Base on the generation process of offset face-gear, the analytical geometry of the offset face-gear drive is derived. The conditions of undercutting and pointing for offset face-gear are studied, the expressions of inner radius and outer radius able to avoid undercutting or pointing are presented. The effects of the tooth number of the shaper, gear ratios and offset distance on undercutting, pointing and tooth face width of offset face-gear are analyzed, respectively. The expressions of approximate solution for inner radius and outer radius are provided.