Abstract: A crystal plasticity model exhibiting deformation twinning is introduced based on the classical crystal plasticity theory,and its numerical implementation is conducted in which a fully implicit integration procedure is employed. In this constitutive model,the saturation-type hardening law is adopted and the direct proportion relationship between twin resistance and slip hardening is used to describe the effect of twinning on slip hardening and twin hardening. By considering the physical meaning of all the 13 parameters in this model,the classification methodology is presented for these parameters. Taking Fe-22Mn-0.6C twinning induced plasticity(TWIP) steel as an example,a local sensitivity analysis of hardening parameters is investigated emphatically. The effects of hardening parameters on the macro-mechanical response,the activation and evolution of twinning and the strategy for determining the hardening parameters are discussed. According to the difference of deformation mechanisms,the macroscopic deformation are divided into a twin hardening stage and a twin hardening failure stage. And then the determination method and the suggestive ranges for the hardening parameters are given. It is found that the initial slip resistance is linearly associated with the yield limit,and the value of initial resistance stress ranges from 80 MPa to 160 MPa. The twin hardening stage weakens when the twin hardening index increases,the range of values allowed for the twin hardening index is 0 to 3. When the ratio between twinning resistance and slip resistance increases,thegrowth rate of twinning decreases and the turning point of the hardening stage moves backward until it is disappeared. The range of values for the ratio between twinning resistance and slip resistance will be 1 to 1.3.