The invention discloses a bridge expansion joint covering mechanism with adjustable tightness, which is used for covering a road surface at a bridge expansion joint. The bridge expansion joint covering mechanism with the adjustable tightness comprises a rubber body (9) which is flush with the horizontal level of a bridge road surface, a supporting body (8) which is positioned in the rubber body (9), and two extending supporting pieces (7) which can move in directions facing each other and opposite to each other in the supporting body (8) and are mutually symmetrical in structures, wherein each of the two extending supporting pieces (7) comprises a horizontal extending head part (721) which can horizontally slide in a sliding chute (81) of the supporting body (8), a vertical extending part (72) which is connected with the horizontal extending head part (721), and a supporting arm (71) which is connected with the lower end of the vertical extending part (72) and extends towards an adjacent bridge structure body, wherein a supporting disc (73) which is used for being connected with the adjacent bridge structure body in a propping manner is arranged at each end part of each of the two extending supporting pieces (7).