Abstract: In order to recover the coal under end slope after mining, theoretical analysis, creep test, numerical simulation and engineering practice are used to study the stability of supporting coal pillar under the condition that highwall machine recovers the coal by the way of holing. With west end slope of Huolinhe North Mine as the engineering background, the necessary condition for the instability of coal pillar is deduced based on mutation theory.The concept of target time strength is put forward based on the service time of supporting coal pillar, supporting coal pillar three days target time strength parameters are determined.Numerical simulation was applied to study coal pillar stability by calculating the range of tensile and shearing plastic zone, reasonable width of coal pillar is determined.Results show that the necessary condition for the instability of coal pillar is the width of the plastic zone is 88% of the coal pillar.Supporting coal cohesion is 0.93 MPa and friction is 17.6°. Reasonable width of coal pillar is determined to be 4 m ,which is proved by engineering practice.

Key words: lignite surface mine, highwall mining, catastrophe theory, creep test, target time strength