Abstract: For the analysis of plastic flow and necking development of the materials with both work hardening and Strain-rate sensitivity under uniaxil tension, this paper proves that the basis of Hart’s analysis is as same as Hutchinson etal’s analysis based on constitutive law b＝Kε{sup}nεThen, based on Hart’s analysis，the flow stability and the criterion of stability of Hart and Jonas etal are discussed. Also, considering the initial geometric imperfection（a0），the incremental and the integral analysis are given for necking development respectively. From the increment analysis, relation between the total elongationδand m as well n are given as；The result of the integral analysis is as same as the integral expression (when n=0)derived by Hutchinson etal. Comparing these theorial results with experimen Tal resnlts, the coincidence is good, In addition, the load analysis is made and two load expressions are given,one is for constant L, the other is for constant.