Abstract: A numerical solut ion for a backward facing step flow(BSF)by the action of lower-wall slipping is simulated with the hybrid finite analysis method.Based on the comparison of the computed results between lower wal slipping BSF and typi cal BSF,the flow configuration effected by lower-wall slipping is analyzed.The comparison displays that the lower-wall slipping BSF has more complicated vortex structure with three vortexes in its flow region.Two small vortexes locate the lower with their lengths decreasing mainly with the increase of lower-wall slipping speed;one large exists in the upper and it lengthens with the increase of both lower wal slipping speed and the Reynolds number,but is more significantly af ected by the Reynolds number.