Viscous models such as Bird-Carreau, Cross, modified Cross, Carreau-Yasuda and Power are often used in commercial software. In order to get the most suitable model, a series of rheological tests were carried out in this study, and a model fitting method based on least square approach was proposed. Combined with the WLF equation related to temperature, these five viscous models were fitted by the fitting method proposed in this paper. The calculated results of the fitted models are compared with the experimental data. The results show that, of the investigated five models, the Carreau-Yasuda and Cross type models can better describe the rheological characteristics of ABS, the Bird-Carreau model is the second, and the Power model is the poorest one. The fitted models are in good agreement with that by Polymat. Some models such as Cross and Power models fitted by the proposed method are even better than that by Polymat.