The mast is an important part of the drill. This paper describes the structural design of the mast of the 4000m core drill independently developed by Institute of Exploration Technology. In order to ensure that the mast meets the requirements of working conditions such as strength， wind load， the mast model is created with SolidWorks， and ANSYS Workbench is used to carry out the finite element analysis for the mast assembly to verify the strength and rigidity of the mast structure， and perform the modal analysis to obtain the first 10 intrinsic vibration frequencies and modes. They are compared with the excitation sources， and the results show the first and second intrinsic frequencies overlap with the frequencies of the drilling turntable and hoisting system， which may cause resonance； thus， the rotating speed of the drilling rig turntable and hoisting system is adjusted to avoid resonance. As a result， the deformation amount is small at the maximum deformation position during vibration， indicating that the mast structural design is reasonable， and can meet the actual application requirements； therefor it has some value in engineering application.