Abstract: A tunnel supporting force adjusting device, comprising a fixed component, a movable supporting component and a driving component, wherein the fixed component is connected with section steel; the movable supporting component is connected with the fixed component and used for connecting with a tunnel trunk, and the movable supporting component, the fixed component and the section steel are fixedly connected with the tunnel trunk by pouring; and the driving component is detachably connected with the fixed component and the movable supporting component respectively to adjust the supporting force of the movable supporting component on the tunnel trunk. The present invention also discloses a tunnel supporting force adjusting method, in which adjusting devices are arranged in different positions of the section steel of the arch section of a tunnel to achieve fixed-point adjustment of the force in each position so as to form optimum supporting force and supporting effect.