Abstract: Air and foam drilling fluid sy stem has much more advantages than the conventional drilling fluid,for it enhances penetration rate and has good lost circulation control ability.The penetration rate by air dust drilling in the hard and dry formation can reach 16.24m/h,while it is 13.16m/h by mist drilling when the formation water production is low,and it is 6.52m/h when the formation produces more water and the pressure is relatively higher,which is comparable with that of foam drilling with penetration rate of 5.23~6.63m/h.However,slight corrosion can be caused on drill pipe by foam drilling,while mist drilling can lead to serious corrosion.Thus suitable drilling fluid should be selected based on the formation conditions,so that the results of improving penetration rate and protecting drill pipe can both be achieved.