The invention discloses a mechanical servo control method for axial-flow threshing. An axial-flow threshing machine with the servo feedback control function is used for applying threshing operation, the natural guide effect is achieved through gravity, and the electric power cost and the labor cost are effectively reduced; meanwhile, a transmission shaft is driven by a motor to rotate, a rolling cylinder shell thus rotates, three crushing bars arranged on the rolling cylinder shell rotate to thus achieve threshing operation, the threshing force in the threshing operation process can be adjusted as required, the operation maximum load force after adjustment is linked with a servo feedback control mechanism through an operation part to achieve the uniformity in the whole threshing process, and it is effectively reduced that due to non-uniform threshing force, seeds after threshing are damaged; with changing of the external feeding amount, the whole servo feedback control mechanism is inthe dynamic balance state, and the whole threshing operation effect is effectively guaranteed; when the abnormal condition occurs in the threshing process, a power control operating lever provides feedback control power for the servo feedback control mechanism so that it can be avoided that the abnormal condition is further extended.