The invention relates to a method and a device for on-line detection and adjustment of the assembly height of a magnetic suspension support. The device is arranged on a height detection working position of an assembly line of the magnetic suspension support, and comprises a machine frame, a hydraulic oil cylinder, a pressure sensor and a displacement sensor. The on-line detection method is implemented by the device and comprises the following steps: when moving to the height detection working position, the magnetic suspension support stays at the position for a plurality of seconds and controls the hydraulic oil cylinder to move vertically upward; after the hydraulic oil cylinder slowly presses against the magnetic suspension support, the oil cylinder is comprehensively controlled to do work by the pressure sensor; when the assembly gap of the support is removed, the reading L of the displacement sensor is converted into the actual height(H1) of the support; and the error value(|delta|) between the actual height(H1) and the rated height(H) of the support is obtained through comparison. According to the error value (|delta|), the leave-factory height of the magnetic suspension support is adjusted. Compared with prior art, the height detection method eliminates the high error factors due to the assembly gap and gets close to the actual working conditions of the support, thereby making the late linear adjustment of a magnetic suspension track beam more convenient.