Pillar width and backfill self-sustaining height are two significant factors in the stage-delayed backfill. A mechanical model for the stage-delayed backfill pillar is established and analyzed on the basis of the elastic plane strain assumption. Taking an iron mine for example, the control variable method (CVM) is used to predict the trends of horizontal stress and shear stress of pillars with different widths and heights. The research results show that: (1) The maximum width and height of the room are 19.8 m and 103.2 m respectively. Horizontal stress of the cemented tailing-filling pillar increases with the increase of pillar height. (2) Shear stress reaches the maximum value at the pillar center, and increases continually with increasing pillar height. When the pillar widths are 15, 18 and 20 m, the corresponding shear stresses are 243.8, 292.6 and 325.1 kPa. The primary reason of the caused shear stress is that the sliding friction occurs on the contact surface of the backfill pillar and the spacer pillar under horizontal stress conditions.