In the geothermal resources exploration and evaluation project in the main urban area and the eastern new urban area of Zhengzhou City， the Neogene Minghuazhen Formation and Guantao Formation is the target layer， where the problem of unstable coring quality exists in the early stage of exploration. Through the analysis of geological and engineering factors which affect the coring quality， it was found that the early used Chuan7-4 type single move double tube coring tool with slip-collar type core gripper is difficult to adapt to the Neogene strata which is of large difference of cementation degree， complex and changeable. In view of the factors that affect the coring quality， calcified mud was used， drilling parameters were optimized， structure of the drilling bit was improved， double action core gripper with card plate and slip-collar was designed and processd. As a result， the coring rate was effectively improved and the problem of instable coring quality was solved in the subsequent exploration construction.