Hollomon’ s equation is deduced from the state equation of plastic tensile deformation and the material constant and the strain hardening exponent in the equation are defined. The measuring formulae are put forward under three typical deformation conditions, i.e. constant strain rate, constant velocity and constant load. This paper also offers the traditional measuring method, the computer simulating measuring method and the exact measuring method corresponding to every formula, and the measuring results on the typical material Zn5%AI at 18℃ and 340℃ are given under three typical conditions. Due to the large deviation among these results, it is argued that the strain hardening exponent is closely related to the forming condition, even in the same stress state. Thereupon, new problems of how to explain the deviation and what is its mechanical essence are raised. Hollomon’s equation is deduced from the state equation of plastic tensile deformation and the material constant and the strain hardening exponent in the equation are defined. The measuring formulae are put forward under three typical deformation conditions, ie constant strain rate, constant velocity and constant load. This paper also offers the traditional measuring method, the computer simulating measuring method and the exact measuring method corresponding to every formula, and the measuring results on the typical material Zn5% AI at 18 ° C. and 340 ° C. are given under three typical conditions. Due to the large deviation among these results, it is argued that the strain hardening exponent is closely related to the forming condition, even in the same stress state. Thereupon, new problems of how to explain the deviation and what is its mechanical essence are raised .