In order to improve the performance of the wire-line coring hydro-hammer in complex formation and to improve the ability of solid-free drilling fluid to maintain the stability of hole walls， the PVA1788 flushing fluid treatment agent was added to tje PHP + GSP solid-free drilling fluid system. When the ratio of PHP， GSP and PVA1788 was 1∶5∶5 and the dosage of mixed powder was 1% to 1.5%， the solid-free drilling fluid performance was as below， APl water loss 10 to 11mL， funnel viscosity 18.4 to 21s， plastic viscosity 3.5 to 6mPa.s， yield stress 0.5 to 0.75Pa. Test and field application showed that the PVA1788 solid-free drilling fluid system had the characteristics of low viscosity， strong inhibition and anti-sloughing ability， good lubrication performance， and convenient operation and maintenance etc.； thus greatly improving the service life of hydro-hammer parts， increasing the drilling capability of drilling rig， and meeting the needs of maintaining stability of hole walls and safe drilling in complex formations. This paper has reference value for the popularization and application of the solid-free drilling fluid in similar formations.