Abstract: Gas drilling is a new drilling method which is developed in the past few years. It has been used more and more widely because it can enhance the ROP, prevent hole leakage, and protect reservoirs. However, air drilling is poor in carrying cuttings and cleaning boreholes as compared with the mist/foam drilling and conventional drilling. So air drilling will not be carried out fast if the borehole can not be cleaned effectively. In this paper, some methods to determine the hole cleaning degree are introduced, based on the standpipe pressure, the clearance pipe pressure, the state of clearance pipe outlet, and the voice of clearance pipe. Field application shows that these methods can non only be used to find out the problems in hole cleaning, but can be used to determine the causes of poor hole cleaning. They lay solid basis for developing reasonable treatment measures.