Abstract: There is a few of measured data of the overlay broken for mechanization caving mining face,especially for the face beneath the unconsolidated lay.The paper introduces the exploration result,by transient electromagnetic method,of the overlay broken on the seam mechanization caving mining face both in the deep district with rock pillar height over 69m and the lower district with the rock pillar height of 28~69m.The results show that the height of the fractured zone in the lower district less 17%~27% than that in the deep district;the variation of the caving zone heights in both districts is not obvious.