The high-value utilization of low-rank coal would allow for expanding energy sources, improving energy efficiencies, and alleviating environmental issues. In order to use low-rank coal effectively, the hypercoals (HPCs) were co-extracted from two types of low-rank coal and biomass via N-methyl-2-purrolidinone (NMP) under mild conditions. The structures of the HPCs and residues were characterized by proximate and ultimate analysis, Raman spectra, and Fourier transform infrared (FT-IR) spectra. The carbon structure changes within the raw coals and HPCs were discussed. The individual thermal dissolution of Xibu (XB) coal, Guandi (GD) coal, and the biomass demonstrated that the biomass provided the lowest thermal dissolution yield Y₁ and the highest thermal soluble yield Y₂ at 280°C, and the ash content of three HPCs decreased as the extraction temperature rose. Co-thermal extractions in NMP at various coal/biomass mass ratios were performed, demonstrating a positive synergic effect for Y₂ in the whole coal/biomass mass ratios. The maximum value of Y₂ was 52.25wt% for XB coal obtained with a XB coal/biomass of 50wt% biomass. The maximum value of Y₂ was 50.77wt% for GD coal obtained with a GD coal/biomass of 1:4. The difference for the optimal coal/biomass mass ratios between XB and GD coals could be attributed to the different co-extraction mechanisms for this two type coals.