Abstract: According to testing modal analysis and spectrum analysis theories, the frequency response curves of ZJ70D drilling rig were obtained by means of dynamic testing in operational conditionals only using the ambient excitation's response, and the first 20 orders natural frequency were identified. The result of the testing indicated that the rotary was the major factor of causing the vibratory of rig derrick and substructure，and oblique upright were weak link of total system. Current vibration problem can be remitted by improving the concentricity of rotary and square-drive master bushing.

Key words: rig, vibration, modal, testing, ambient excitation