Agitation power consumption (P) in the anaerobic digestion of biogas plants is a major part of the electric energy consumption. To reduce P by adjusting the rheological properties, in this work, the rheological properties of corn straw slurry were studied systematically with the consideration of the effects of TS, temperature and particle sizes. The P was calculated based on the rheological behaviour of corn straw slurry. The investigation shows that the thermophilic digestion is effective only for the slurry with a relatively high TS. The size-reduction is more effective at higher TS compared to the option of increasing temperature in order to improve the agitation power efficiency, and the value of P can be reduced by up to 48.11 %. Since the size-reduction can also increase the methane yield, the adjustment of particle sizes is a promising option to save P, especially at higher TS.