Scientific drilling is an important technical means for obtaining underground physical data， anaylzing underground structures， and verifying important geological theories. The key underground instrument is an important basic guarantee for ensuring the smooth implementation of drilling projects. However， during the myriametric scientific drilling process， the requirements of underground working conditions and craftwork such as high temperature， high pressure， long drilling period， and large specification parameters seriously challenge the working performance of underground instrument. To the end， this paper analyses the structural characteristics and failure reasons of key underground instrument such as drill string， downhole mud motor， and auxiliary synergistic tools under the myriametric drilling working condition， and proposes corresponding measures on optimizing the structure of drill pipe joint， designing metal gear drill， improving the structure of hydraulic oscillator and injection-type torque thruster， and materials selection and setting up surface strengthening techniques， which can provide technical reserves for earth interior detection.