This article introduces field use of small-diameter wireline core drilling for geothermal survey hole ZK01 in the northern part of Dangshan County， Anhui province， where water-sensitive mudstone formation with a thickness of more than 600m was encountered. The mudstone was hydrated at the surface after encountering water， leading to the diameter shrinkage and the thick mud cake on the inner wall of the casing， which resulted in poor mud circulation and mud pump choking. In light of the characteristics of the small-diameter rope core drilling process， with analysis of the hole shrinkage characteristics and the causes for the mud cake on the inner wall of the casing， hydraulic control reaming drill bits were used with non-solid emulsified inhibitive drilling mud to achieve good results. The article describes the principle of the hydraulic control reaming bit， the precautions for reaming operation， the maintenance and preparation of non-solid emulsified inhibitive mud. The hydraulic control reaming bit was used for the first time in the small-diameter wire core drilling process， which can provide a good reference for subsequent drilling in similar formations.