Abstract: The compress experiment of 4 aluminum alloys is made by means of a Can Plastometer with constant strain rate. The flow stress is meassured under cold deformation. 5 types of mathematic model of flow stress are analysed and compared. The effect of deformation conditions on flow stress is discussed. And the best mathematic model of flow stress is obtained.Its construction is simple, its accuracy is high, and it is suit for the use of on-line control of computer.