The chemical absorption method with N-methyldiethanolamine（MDEA） + piperazine（PZ） aqueous solution as the composite absorbent is one of the important means for CO,2, capture. However, the high regeneration energy consumption of this composite absorbent limits its application in the field of carbon capture. In order to overcome this shortcoming, some certain additive is added to form phase change absorbent to reduce the total amount of absorbent into the desorption unit, so as to reduce the energy consumption for regeneration. A liquid-solid phase change absorbent with the composition of MDEA + PZ + N-methylpyrrolidone（NMP） + water（H,2,O） was designed. The CO,2, absorption performance of the liquid-solid phase change absorbent was investigated, the effects of mass fraction of NMP and PZ on the CO,2, solubility were determined, and the mechanism of liquid-solid phase separation behavior mechanism was also analyzed. The results show that, the CO,2, solubility of the liquid-solid phase change absorbent decreases with the increase of the mass fraction of NMP and increases with the increase of the mass fraction of PZ. When the mass fraction of NMP and PZ in the absorbent reaches 50% and 3% and above, respectively, the PZ-carbamate formed by absorbing CO,2, can reach saturation and precipitate to form a solid phase. The solid phase first increases with the increase of CO,2, solubility, and then PZdicarbamate which is more soluble in water is formed with the increase of CO,2, solubility, resulting in the decrease of solid phase.