Usually model parameters from uniaxial experiments are not suitable for dielectric elastomer under biaxial loading condition. To characterize the mechanical behavior of dielectric elastomer, a biaxial tensile bench is established, on which uniaxial tests can be performed too. On the basis of the analysis of viscous effect of elastomer, experimental condition for data acquirement is determined. Then equi-biaxial and uniaxial experimental data are obtained to fit three constitutive models, i.e. Mooney-Rivlin, Yeoh and Ogden model. Also, least square minimization method is used to obtained model parameters, which are applicable to both uniaxial and equi-biaxial experimental data.