In recent years, non-aqueous absorbents have attracted increasing attention due to their ability of significantly reducing sensible and latent heats in regeneration processes compared to conventional organic amine aqueous solution. But high viscosity of non-aqueous absorbents after CO2 absorption saturation became an obstacle to their industrial application. Here, a novel low-viscosity diamine non-aqueous absorbent for high-efficiency CO2 capture was proposed, in which N-methyldiethanolamine (MDEA) with steric hindrance effect was introduced as a regulator and dimethyl sulfoxide (DMSO) as a cosolvent. The effects of MDEA on CO2 capture performance of various non-aqueous absorbents and its regulation mechanism on CO2 absorbent viscosity were investigated systematically. Experimental results showed that when 25 wt% 2-(2-aminoethylamino)ethanol (AEEA) was screened as main CO2 absorption component, AEEA/MDEA/DMSO non-aqueous absorbent exhibited a high CO2 absorption capacity of 2.55 mol/kg and a fast CO2 absorption rate. Based on further mass fraction optimisation, it was found that the lowest viscosity of non-aqueous absorbents after CO2 absorption was 13.12 mPa s and the highest CO2 regeneration reached 93.5 % with AEEA and MDEA were 17.5 wt% and 12.5 wt%, respectively. 13C NMR tests showed that two characteristic peaks of carboxylated carbon appeared in CO2 products, which indicated that both amino groups on AEEA molecule were involved in CO2 absorption reaction. DFT calculations indicated that hydrogen bonding strength between MDEA and CO2 products was relatively lower than that of AEEA and CO2 products, which favored reducing absorbent saturation viscosity significantly. Thermodynamic analysis revealed that total regeneration energy consumption for 17.5 wt% AEEA/12.5 wt% MDEA/70 wt% DMSO non-aqueous absorbent was 1.72 GJ/t CO2, which was 53 % lower than that of MEA aqueous solution.