Abstract: T he mistake of strata comparison between designed boundary and the real boundary by well completion of wellYHD-1 in 2002 in Qaidam Ba sin was made, its reason would be the result of continuing to use the wrong data of stra ta division from well Yanshen-1(1959) and well Yan-14(1995). Agip's summary report of well completion said tha t the aim bed drilled would be Pa leocene-Eocene Lulehe Forma tion, but the authors keep opposed opinion tha t the a bov e boundary is still drilled into Miocene Xiayoushasha n Forma tion. T he a ge value of stratum a t well bottom estimated by both parties ha s la rger difference, which is at lea st the discrepancy of 26Ma, accounting for second fifth of Cenozoic era(65Ma ).On the basis of analysis on the cause of false comparison byAgip Company, it sets forth that the comparison of Cenozoic strata of Qa idam Ba sin, which fea ture in complex sedimentary structure and multiple material sources, should be adopted comprehensive correla tion method, especially integrating seismic stratigra phy with biological stra tigraphy method.

Key words: design of exploration well, stratum comparison, seismic strata, biologica l strata, Qaidam Ba sin