A covered stent suitable for fixing an external branch stent comprising a tubular main stent and a connection stent disposed on the main stent , an opening (O) being formed in a side wall of the main stent , wherein the connection stent comprises a fixed segment connected to the side wall of the main stent and a free segment connected to the fixed segment , each of the fixed segment and the free segment comprising a stent and a coating covering the surface of the sent, one end of the free segment distant from the fixed segment being connected to the edge of the opening (O) and a gap being formed between one side of the free segment near to the side wall of the main stent and the side wall of the main stent , characterized in that the stent of the free segment comprises a plurality of waveform rings , any two of the adjacent waveform rings being opposite in phase, and the crests and troughs of any two of the adjacent waveform rings being interlocked, and the crests or the troughs of at least two of the waveform rings at the fore and aft ends of the stent being connected to the coating of the free segment , wherein the plurality of the waveform rings comprise a first waveform ring , a second waveform ring spaced apart from the first waveform ring, and a third waveform ring provided between the first waveform ring and the second waveform ring and connected to the first waveform ring and the second waveform ring, the third waveform ring having an unequal height waveform, wherein an apex of the crest of the third waveform ring comprises a first crest near to the first waveform ring and a second crest distant from the first waveform ring, and the first crest and the second crest being spaced circumferentially along the third waveform ring and falling on two planes perpendicular to an axis of the third waveform ring, respectively, and the apex of the trough of the third waveform ring falling on the same plane perpendicular to the axis of the third waveform ring, the crest near to the first waveform ring being interlocked with the trough of the first waveform ring, and the trough of the third waveform ring being interlocked with the crest of the second waveform ring . characterized in that the stent of the free segment comprises a plurality of waveform rings , any two of the adjacent waveform rings being opposite in phase, and the crests and troughs of any two of the adjacent waveform rings being interlocked, and the crests or the troughs of at least two of the waveform rings at the fore and aft ends of the stent being connected to the coating of the free segment , wherein the plurality of the waveform rings comprise a first waveform ring , a second waveform ring spaced apart from the first waveform ring, and a third waveform ring provided between the first waveform ring and the second waveform ring and connected to the first waveform ring and the second waveform ring, the third waveform ring having an unequal height waveform, wherein an apex of the crest of the third waveform ring comprises a first crest near to the first waveform ring and a second crest distant from the first waveform ring, and the first crest and the second crest being spaced circumferentially along the third waveform ring and falling on two planes perpendicular to an axis of the third waveform ring, respectively, and the apex of the trough of the third waveform ring falling on the same plane perpendicular to the axis of the third waveform ring, the crest near to the first waveform ring being interlocked with the trough of the first waveform ring, and the trough of the third waveform ring being interlocked with the crest of the second waveform ring . <EOS>