The technical scheme provides a modular and dismountable movement mechanism for a linear multidigit ionization chamber, which comprises a guide shaft fixed on a bottom board, a limit lever assembly, a microswitch, a load frame capable of making linear displacement with a transmission rack, a limit lever, a pressure spring, the ionization chamber arranged on the load frame and the like. The limit lever assembly comprises a positioning bearing, a universal rotating head, a torsional spring, a torsional spring connecting rod and the like; and a limit slot is formed on the limit lever fixed on the load frame. When the positioning bearing just moves to a slope of the limit slot and does not stop in the limit slot, the microswitch corresponding to the limit slot is pressed, a motor stops operating, and the torsional spring and the pressure spring push the load frame with the ionization chamber together to continue to move, so that finally the positioning bearing slides into the limit slot completely, the load frame stops moving, and a station is adjusted in place. The mechanism is arranged below a turnplate of a beam flattening filter of an accelerator to measure the intensity of radiation passing through the flattening filter, and is convenient to overhaul.