The invention relates to the technical field of oil and gas drilling, well completion, well cementation or well logging, in particular to an external casing packer. The external casing packer comprises a center pipe, a rubber sleeve and a rubber sleeve fixing ring, the rubber sleeve is arranged outside the center pipe in a sleeving mode, the rubber sleeve fixing ring is fixed to the center pipe and fixedly connected with the two ends of the rubber sleeve, and an annular space is reserved between the rubber sleeve and the center pipe. The rubber sleeve comprises an inner sleeve made of an elastic material which does not expand when encountering liquid and an outer sleeve made of an elastic material which expands when encountering oil, a first flow channel leading to the annular space is formed in the rubber sleeve fixing ring, and a sealing valve element is arranged at an inlet of the first flow channel; and the inner sleeve comprises an inner sleeve body, a radial through hole is formed in the axial center of the inner sleeve body, a fracturing sealing film is arranged at the end, facing the center pipe, of the through hole, and a finger-shaped reed is arranged at the joint of therubber sleeve and the rubber sleeve fixing ring in a surrounding mode. The external casing packer can prevent the rubber sleeve from bursting, tearing and extruding, and the packing effect is improved.