There is an urgent demand to explore advanced solvents for CO2 capture considering the defects associated with traditional alkanolamine-based solvents. In this work, tetraethylenepentamine (TEPA) was selected as the key component, while 1-ethyl-3-methylimidazolium acetate ([emim][AcO]) was selected as the chemical diluent and supplementary component to construct the mixed solvents for CO2 absorption based on the concept of "chemical solvent in chemical solvent". The CO2 absorption rates and capacities of mixed solvents were experimentally investigated. Impressively, the CO2 capacities reach a value of 3.41 mol/kg at 313.2 K and 15.0 kPa for TEPA + [emim] [AcO] (0.2:0.8), surpassing those of most other solvents reported in the literature. Furthermore, a dual-site reaction equilibrium thermodynamic model equation was derived to correlate the CO2 capacities and calculate the reaction equilibrium constants and enthalpy changes of CO2 absorption. On the basis of the experimental and thermodynamic analysis, it is believed that TEPA + [emim] [AcO] mixed solvents are promising candidates for the capture of CO2 from flue gas.