Abstract: Nowadays, the Wenner device of high-density electrical method has been used more and more widely in engineering. It is very significant to study its detecting depth of boulders in ground. This paper analyzes the factors influencing the detecting depth in detail. It studies the basic theory to the Wenner device in depth and then gets the relationship between the detecting depth and the four primary factors including agitation error, abnormal body radius, relative resistivity of abnormal body and electrode spacing. The research results show that, the detecting depth of Wenner device decreases with the increase of agitation error and increases nonlinearly with the increase of abnormal body radius. When the relative resistivity value is about one, the detecting depth is minimized. But when it increases to a certain value, the detecting depth does almost not change. When other factors are unchanged, the detecting depth increases with the increase of electrode spacing, which will reduce if the electrode spacing has exceedingly increased. Finally, by combining the theoretical analysis with field results, this paper proposes a method to improve the detecting depth of Wenner device to boulders based on the numerical simulation.