Whilst composite materials have been widely used in aeronautic applications, reinforcement of openings caused by functional requirements such as facility maintenance and equipment installation should be necessarily considered, especially for composite panels with an Abnormal Large Opening (ALO), which will cause severe stress concentration and even premature structure failure. This paper presents an experimental investigation of the tensile properties of composite panels with an ALO after reinforcement. Tensile tests of the original structure, structure with the cover removed and reinstalled were carried out to verify the efficiency of reinforcement and repeated disassembly performance of the cover. Strain measurements were synchronized simultaneously in all tests above, whilst the influence of the opening and the cover on the loading transfer path was discussed based on the test strain data. Test results showed a significant reduction of stiffness when the cover was removed compared to the original structure and the structure with the cover reinstalled. Barely Visible Impact Damage (BVID) was introduced in the failure test of the last specimen, and the influence of BVID on the failure form and bearing capacity of ALO structures was discussed.