BTA (Boring and Trepanning Association) deep hole drilling is a widely applied cutting method to manufacture or process bores. In this thesis, numerical simulations with Finite Element Method for the determination of eigenfrequencies of a BTA deep drilling machine in real boundary and working conditions are executed with Ansys Workbench in order to study dynamic disturbance during deep hole drilling processes. The pre-stressed modal analysis gives the information regarding varying dominant eigenmodes and the corresponding critical locations on the boring bar of BTA tool with different drilling depths. To prevent chatter vibration and spiralling during the deep hole drilling process, a real-time monitoring of varying system dynamics would be recommended and the results from the simulation are considered as reliable references in this case. Furthermore, the influences of the one-way Fluid-Structure Interaction, drilling-depth dependent values of boundary conditions and material damping effect are proven not to be neglected comparing to the influence of mechanical loads on BTA tool head in modal analysis.