Abstract: The chain structure of several polyolefin elastomer (POE) samples was characterized by GPC and NMR, and their melt flow stability at high extrusion rate and their melt viscosities at various shear rates and temperatures were investigated by capillary rheometer. The relationship between the chain structure and melt viscosity were further analyzed. The results indicated that there was an unstable flow in the polymer melt with higher molecular weight with an increase of shear rate, and the surface of the melt extrudate became distorted. The critical shear rate also becomes lower if the molecular weight and co-monomer content were higher and the temperature was lower. The shear viscosity of POE was greatly influenced by the molecular weight and was almost not related to the co-monomer content. The polymer melts with various molecular weights and their compositions have the approximately same viscous flow activation energy around 2.8×10^4 J/mol. Based on the Carreau Equation, Cross Equation and Arrhenius Equation, the semi-model correlated with the zero shear viscosity, weight-average molecular weight and temperature and the semi-model related to correlated with the melt apparent viscosity, zero shear viscosity and shear rate were established. Both of the two equations are available to predict the melt viscosity of POE in the temperature range of 130~190 ℃, in the shear rate range of 10~2 000 s-1, in the weight-average molecular weigh range of 4.2×10^4 ~1.24×10^5 g/mol.