A belt tensioner to be applied to a bike , the bike comprising a frame and a belt , the frame comprising a chain stay and a seat stay , the chain stays and the seat stay respectively having a top surface and a bottom surface , the belt tensioner comprising: a tensioner skeleton pivotally connected to the chain stay wherein an included angle (A) is formed between the tensioner skeleton and the chain stay ; a roller pivotally connected to the tensioner skeleton and being in contact with the belt ; and a tension regulator for pressing against the belt so as to adjust a tension of the belt , wherein the tension regulator is disposed at an end of the tensioner skeleton , and the end of the tensioner skeleton is positioned distal to the bottom surface , wherein a part of the belt is in contact with the tension regulator , and wherein a vertical height the contact part of the belt greater than a height of the top surface , when the tension regulator presses against the belt ; wherein the tensioner skeleton further comprises a first link and a second link , the first link being disposed at the chain stay and having a first extension direction (D1), and the second link comprising a first end pivotally connected to the first link , wherein the second link has a second extension direction (D2) when the first end is pivotally connected to the first link , and the included angle (A) is formed between the first extension direction (D1) and the second extension direction (D2); wherein the second link comprises a second end , and the second end is pivotally connected to the roller ; characterized in that the tension regulator further comprises a positioning holder and an elevating stud , the positioning holder being connected to the tensioner skeleton , and the elevating stud being movable relative to the positioning holder and being able to increase the tension of the belt by moving upward to press against the belt . a tensioner skeleton pivotally connected to the chain stay wherein an included angle (A) is formed between the tensioner skeleton and the chain stay ; a roller pivotally connected to the tensioner skeleton and being in contact with the belt ; and a tension regulator for pressing against the belt so as to adjust a tension of the belt , wherein the tension regulator is disposed at an end of the tensioner skeleton , and the end of the tensioner skeleton is positioned distal to the bottom surface , wherein a part of the belt is in contact with the tension regulator , and wherein a vertical height the contact part of the belt greater than a height of the top surface , when the tension regulator presses against the belt ; wherein the tensioner skeleton further comprises a first link and a second link , the first link being disposed at the chain stay and having a first extension direction (D1), and the second link comprising a first end pivotally connected to the first link , wherein the second link has a second extension direction (D2) when the first end is pivotally connected to the first link , and the included angle (A) is formed between the first extension direction (D1) and the second extension direction (D2); wherein the second link comprises a second end , and the second end is pivotally connected to the roller ; characterized in that the tension regulator further comprises a positioning holder and an elevating stud , the positioning holder being connected to the tensioner skeleton , and the elevating stud being movable relative to the positioning holder and being able to increase the tension of the belt by moving upward to press against the belt . <EOS>