The macro-plasticity power function constitutive model(MPFCM), the modified macro- plasticity power function constitutive model(MMPFCM) and the micro-plasticity constitutive model(MCM) taking the material intrinsic length were established to characterize the microindentation size effects of pure aluminum, respectively. The experimental results indicated MPFCM only determined precisely in the great indentation load. While a modified one named MMPFCM was subsequently established taking account of the parameters variation with the increase of indentation depth. The conventional dimensional analysis method was employed to determine the strength coefficient K and the strain hardening exponent n of this modified model. And then MCM taking account of size effects was proposed based on the Taylor dislocation model. The first- order steepest gradient descent method was adopted to obtain the material intrinsic length for the geometrically necessary dislocations. The parameters of MCM were identified by using the UMAT subroutine of ABAQUS software. The average absolute relative error of MCM is relatively lower than that of the macro-one. Although the precision of the modified one is also high, the applied scope is limited, only for the microindentation material. In addition, the intrinsic length 5.09 μm of pure aluminum is also obtained based on the strain gradient theory. The macro-plasticity power function constitutive model (MPFCM), the modified macro-plasticity power function constitutive model (MMPFCM) and the micro-plasticity constitutive model (MCM) taking the material intrinsic length were established to characterize the microindentation size effects of pure aluminum , respectively. The experimental results indicated MPFCM only subsequently established precisely in the great indentation load. While a modified one named MMPFCM was succeeded in establishing account of the parameters variation with the increase of indentation depth. The conventional dimensional analysis method was employed to determine the strength coefficient K and the strain hardening exponent n of this modified model. And then MCM taking account of size effects was proposed based on the Taylor dislocation model. The first-order steepest gradient descent method was taken to obtain the material intrinsic length for the geometrically necessary dislocations. The parameters of MCM were identi fied by using the UMAT subroutine of ABAQUS software. The average absolute relative error of MCM is relatively lower than that of the macro-one. Although the precision of the modified one is also high, the applied scope is limited, only for the microindentation material . In addition, the intrinsic length 5.09 μm of pure aluminum is also based on the strain gradient theory.