Abstract: The local instability of key pillar will induce the chain failure of coal pillar system and the linkage failure of surrounding rock.Identification of the key pillar’s position is the basic premise for the scientific prevention and control of coal rock mass chain failure in the pillar mining gobs.The concept of minimum equivalent width is defined firstly.Four methods are proposed to determine the minimum equivalent width of residual coal pillar with different shapes.The calculation method of coal pillar’s strength is then optimized.By introducing the maximum transferred distance of stress,the bearing load calculation formula of residual coal pillar is improved.Then,the safety factor of each residual coal pillar in the studied area is obtained,and the residual coal pillar with the minimum safety factor can be identified as the key pillar.Lastly,the technical method of key pillar in the residual pillar system are formed.In addition,the KPDS software are developed based on the Python language to make an intelligent assessment on key pillar.The results show that:① the minimum equivalent width means the minimum practical bearing width of residual coal pillar with different shapes.The inscribed circle method,the shortest side method,the auxiliary line method and the short axis method can be used to determine the minimum equivalent width of regular or irregular residual coal pillar.② The inscribed circle method is suitable for determining the minimum equivalent width of triangular and regular polygon residual coal pillar in the gob.The shortest side method is suitable for determining the minimum equivalent width of residual coal pillar with shortest side and parallel adjacent side in the cross section.The auxiliary line method is suitable for determining the minimum equivalent width of residual coal pillar with shortest side and non parallel adjacent side in the cross section.The short axis method is suitable for determining the minimum equivalent width of semicircular,circular and oval shaped residual coal pillar.③ The load acting on the residual coal pillar not only includes the load of overlying strata in the tributary area,but also involves the transferred load of adjacent overlying strata.Considering the maximum transferred distance of stress,the load of residual coal pillar can be calculated more accurately.④ Based on the minimum equivalent width and the maximum stress transferred distance,the residual coal pillar with the smallest safety factor in the gob can be determined and the key pillar can be further identified.The identification technical process for key pillar can also formed.⑤ KPDS is the abbreviation of Key Pillar Determination Software.It mainly includes:login page,parameter importing page,strength comparison calculation page,safety factor determination page and key pillar identification page.KPDS software can quickly and intelligently identify the key pillar in the residual pillar system.The development of key pillar identification methods and intelligent software can realize the pre distinguishment of key pillar position in the residual pillar system,which is expected to guide the scientific prevention and control of residual coal pillars’ chain failure and surrounding rock’s linkage failure.It can also further promote the rock strata control theory in the coal mining field.