Abstract: The movement of the full drillstring is a very complex nonlinear dynamical process.It is impossible to get very much perfect analytic solution and there is high cost of experiment.Thus，based on elasticsplastic mechanics，rock mechanics and drilling string mechanics and the drilling data of some gas well，this paper successfully establishes the complex nonlinear dynamics finite element 3D realtime drilling model of several kilometerslong irregular borehole，and real conditions are considered，such as mutual action between drill bit and rock，unknown contact between tapered drillstring and hole，effect of complicated 3D well trajectories (azimuth angle，deviation angle) and real drilling parameters (WOB，rotating speed).The timevarying data at each point on the long drillstring can be obtained after simulated，including displacement，axial force，stress，bending moment，torque，vibration，and contact force.These data are processed to obtain the perilous stress zones，the severe abrasion areas，the lowest fatigue life section which possibly lead to failure and difference between gas drilling and mud drilling，which can provide theoretical foundations for the application of drillstring failure and prevention.Furthermore，it is useful of this model to study drilling string mechanics，hole deviation control and equipment in air drilling.

Key words: full drillstring, gas drilling, dynamics, FEM, mud drilling