The analytical hierarchy process (AHP) combined with response surface methodology (RSM) was used to optimize the purification conditions of crude polysaccharides from Carex meyeriana Kunth (CMKP) by macroporous resin. The optimal purification conditions as follows: elution volume of 2.74 BV, flow rate of 1.88 BV/h, and sample concentration of 2.10 mg/mL. Under the optimal conditions, the purification comprehensive score was 63.59 ± 1.56% (n = 3), which was agreed closely to the predicted value (64.02%). Two fractions of polysaccharides (CMKP-1 and CMKP-2) were obtained using a DEAE-52 column. Fourier Transform infrared (FTIR) spectroscopy spectra revealed the general characteristic absorption peaks of CMKP-1 and CMKP-2. Congo-red test indicated that CMKP-1 and CMKP-2 have triple helix conformation. CMKP-1 and CMKP-2 were both composed of Man, Rib, Rha, GluA, GalA, Glu, Gal, Xyl, Ara and Fuc in a molar ratio of 8.93:1:4.62:1.41:1.78:10.7:24.69:4.51:15.92:1.27 and 7.85:1:5.05:1.99:3.15:12.47:15.41:1.54:6.91:3.15, respectively. The major molecular weight of CMKP-1 and CMKP-2 was 22.30 kDa and 48.10 kDa, respectively. Moreover, CMKP-1 and CMKP-2 had immunostimulatory effects on RAW264.7 cells in a certain concentration range. It could be used as potential immunomodulatory agents in medicine or functional food fields.