Abstract: In well Gangshen-78, 177 8mm casing is used to isolate the lost circulation area, and subsequent hole must be deepened. The 152.4mm bit designed for slim hole drilling is used in drilling the subsequent hole, so as to increase casing annular space and improve cementing quality. The bit is successfully used in this well, and sets a record of the longest interval drilled using the same kind of bit in China. This paper describes the field using of the bicentral bit and drilling fluid treating on field, and summed up 8 items for reference in field drilling.