The utility model discloses an external extension type flexible shielding outer cover adapted to an exposed balcony, which comprises a fixed column and two support columns, the two support columns are arranged on one side of the fixed column, two mounting seats are arranged on one side of the fixed column, the fixed column is connected with the mounting seats through mounting mechanisms, and the mounting seats are connected with the fixed column through the mounting mechanisms. And sunshade cloth is wound in the fixing column through a winding mechanism, a moving plate is arranged at the tops of the two supporting columns, a cover plate is rotationally installed on the outer wall of one side of the moving plate, and a driving mechanism is installed at the top of the moving plate. According to the sun-shading device, when rainfall weather occurs in the external environment, the driving motor can drive the winding roller to automatically wind the sun-shading cloth, water accumulation on the top of the sun-shading cloth is avoided, and after the sun-shading cloth is completely wound on the surface of the winding roller, the groove in the top of the fixing column can be blocked by means of the cover plate, so that the sun-shading effect is improved. The rainwater is prevented from being continuously contacted with the sunshade cloth, so that the service life of the sunshade cloth can be prolonged, and the use durability of the sunshade cloth can be indirectly improved.