Abstract: Based on the investigation of coal deformation characteristics under microscopic scale (optical microscope and scanning electronic microscope)in laboratory,coal brittle ductile deformation is identified in this paper.During geological history,coal suffered from brittle to brittle ductile and ductile deformation under the conditions of tectonic stress field.Griffith Cracks or fractures are formed as a result of brittle deformation.Brittle ductile deformation is an intergrading style.Typical coal ductile deformation is concentrated in the mylonitic coal.Almost all characteristics of ductile deformation in rocks are identified in coal,expect for recrystallization.