Abstract: The drill sting for the gas drilling is impacted in the process of crushing rock，so the alternating stress occurre.
Alternating stress changes is aggravated by the rotating drill string，and the drill string is also erosion by debris，so the failure
is accelerated. The main failure form of drill string is fatigue fracture，which is inseparable from the drill string，so the research
on mechanical properties and erosion of the drill string in gas drilling，mastering the drill string stress change rules and erosion
law of drill string are the basic work to reducing and preventing the drill string failure. This work has very important meaning
for increasing the safety and reducing the cost in gas drilling. The drill string of gas drilling in the situation of vibration and
erosion in the case of different combination drilling tools by using an experiment device which can simulate the situation is
studied in this paper. The experiment shows that using centralizer will reduce the alternating stress value range up to 40%，and
using centralizer and shock absorber at the same time will reduce the alternating stress value range up to 50%. The centralizer
and the shock absorber used together will reduce the alternating stress greatly and extend the alternating stress function cycle，
thus the probability of failure of the drill string will be reduced.

Key words: gas drilling, mechanical properties, experimental research, alternating stress, vibration and erosion