The inner pressure creep resistance of two kinds of domestic Mo-Nb alloy single crystal was researched by applying biaxial load on the tube specimen through the inert gas medium. The niobium contents of them were 3wt% and 6wt%, respectively. Results show that the inner pressure creep resistance strengthens, while the steady-state creep rate and the sensitivity to hoop stress drop with the increasing solute niobium atoms. With the increase of niobium content, more multilateral structures of the dislocation form and the shape of the Nb-rich precipitate changes from particle to shaft. These factors induce that the molybdenum atom diffusion become more difficult, and the inner pressure creep resistance of Mo-Nb alloy single crystal becomes more superior.