In the traditional view, the target accuracy derived from the calculation of the drilling trajectory is the actual target accuracy, but along with the development of drilling technology and measurement technology, this concept is gradually broken. There is considerable discrepancy between the target location calculated by mathematical calculation model and the actual location in practical operation, even the target location measured by active magnetic measurement technology is uncertain. With H1-H2 well group as the case, the reasons of this uncertainty are analyzed and active means were adopted to complete the project in the construction.