Abstract: In order to obtain current formation pressure of Yacheng 13-1 Gas Field,verify the producing degree of section 3 in Lingshui Formation,and avoid the risk of conventional wireline logging,StethoScope 675 type tool was used to draw formation fluid for pressure test after Well A9 of the gas field was finished.According to the test data obtained,formation pressure and formation physical parameters were determined,which gave further understanding of the gas reservoir,and guided subsequent production operation.This paper briefly presents the principle,technical features and the testing process of StethoScope 675 type formation pressure test while drilling tool,and Well A9 testing process.