Abstract: In this paper, from the fundamental defination of m value, the formulae of measuring strain rate sensitivity index m with un-extrapolating and extrapolating load jumping meth ^ ds were derived. And the design about measuring instrument and the measuring methods were also given. Through mechanical analysis, the functional relations among mop,me p,, MI, m? and mp were eastablished and proved to be correct through experiments. Through comparison with various kinds of measrring methods in tensile test, it can be concluded that load jumping method is accurate on results, simple on measuring method, and easy to be realized on the measuring instrument. And this method can eliminate the influnce on m value by the, change of material composition during deformation period and by stagnant of loading system. Moreover the loading process of this method is relatively consistant with real forming process. Thus this method may be populized to bulge, extrusion and etc, it also may be used to study the in　flunce on m value by loading styles of load-increase and load-decrease.

Key words: m值测量仪, 应变速率敏感性指数, 应变硬化指数