In order to study and improve the stability and reliability of the mast of rotary drilling rig in the course of construction, in this paper, three-dimensional models of the mast of rotary drilling rig are firstly created by the software of Pro/E, which are accurately built with full consideration of actual geometrical feature of the mast ofrotary drilling rig, and then form a corresponding finite element model so as to carry out an analysis on the bending deformation of the mast of rotary drilling rig by the software of Ansys and to disclose the deformation regularity of the mast of rotary drilling rig and maximum deformation under different working radius. The rational experiment is subsequently applied to prove the accuracy of Ansys for the mast of rotary drilling rig. Finally, the deformation results from the experiment are in accordance with that from the software of Ansys, which approve the forecast capability of FEM simulation for the mast of rotary drilling rig. The method and experience of this paper will provide theoretic supports for more optimization design and research of the mast of rotary drilling rig.