Abstract: A bicycle bottom bracket set has two bearing cups, the bearing cup has a built-in ring, a tightening socket and a bearing. The built-in ring and the tightening socket are provided with a guiding end and a connecting portion. When the bearing cup screw is installed, the guiding end of the built-in ring can be gradually opened and pressed against the inner wall of the bottom bracket. When the bottom bracket has inner diameter offsets caused by the heat expansion and contraction factor or the poor processing, the combination of the forced tension of the bearing cup can achieve the purpose of structurally limiting. The stability of the structural installation while ensuring the safety of the structure.