Abstract: Wilson strength theory has been used widely in coal pillar strength check of strip mining whose result can meet mining requirement．In conventional strip mining，simplified formula of this theory can be used．When mining parameters of two sides of coal pillar were different，flexibility was needed to check coal pillar stability with this theory．This paper introduced main characteristics of unconventional strip coal pillar，from basic principle of Wilson strength theory，the check formula of unconventional strip coal pillar stability was obtained．In practice，this formula was applied to checking coal pillar stability of unconventional strip mining．