Abstract: Based on the working resistance observation of the leg and the balance jack used in the two leg shield coal caving support applied to Shendong Liuta Mi ne, the theoretical support efficiency of the ZFY10200/25/42 type two leg shield coal caving support was analyzed as 83. 1%.During the actual application, due to the te nsion of the balance jack often in an irrational work condition, the support efficiency of the powered support would be highly reduced and the actual support efficiency of the powered support applied in No.08 fully mechanized top coal caving mining face only reached 68.7%.The paper held that the two leg shield caving powered support would not be suitable for the top coal caving mining in the hard coal seam and the joint crack undeveloped medium hard seam.