Abstract: Taking acting force of powered support into account， key block of“cantilever-articulated beam”in roof was analyzed on the basis of " cantilever-articulated beam" structure model. S-R stability conditions of key block were perfected. In order to control sliding instability whose influence on mining face safety was more seriously than rotation instability， working resistance design method was put forward for top-coal caving powered support. Applying this method， a powered support was selected for 8105 mining face of Tashan Colliery. Actual application showed that this powered support adapted its roof condition in a better way.