A comprehensive theoretical model is developed to describe mid-IR laser radiation propagation in an optical cylindrical waveguide. The effects of various parameters of the beam as well as of the waveguide on the output beam shape are studied and analyzed. parameters such as beam coupling misalignment, waveguide diameters, and inner wall roughness are studied. The same conditions are applied in the theoretical calculations as well as in the experiments. Good agreement between the theoretical and experimental results is found.