In presence, going with the exploiture of oil and gas, the engineering has developed toward the direction of super deeper well, the problem of drill-string fatigue has a great effect to drilling engineering. Strong vibration is one of the main reasons. Computer can simulate the system of drill-string, and calculate the problem of drilling movetion. Drill-string of deeper well is object being studied. The models about axial vibration, lateral vibration and torsional vibration are set up. Modal vibrations of drill-string are studied. Rules of all sorts of nature frequency are obtained by drilling instance.This study can prove theory bases for optimizing drill parameter of deeper well and how to reduce drill-string failure.