Haematococcus pluvialis residue powder, which has been extracted with astaxanthin, was used as the raw material to prepare Haematococcus pluvialis protein by alkaline extraction and acid precipitation method. The protein structure of Haematococcus pluvialis was characterized, and the effects of pH and ion strength on the functional characteristics of Haematococcus pluvialis protein were studied. The results showed that the isoelectric point of Haematococcus pluvialis protein was 4.2. The molecular weight of the subunit was around 14.4, 18.4 and 38 kDa, respectively and the content of α-helix, β-fold, β-corner and disordered structure in the secondary structure was 14.86%, 18.47%, 40.3% and 26.37%, respectively. It contained 7 kinds of essential amino acids required by the human body, accounting for 36.38% of the total amino acid content. Microscopic observation showed that the protein of Haematococcus pluvialis was rod-shaped and sheet-like, with a rough and porous surface. With the increase of pH, the solubility, water absorption, emulsion capability, foam stability and foam stability of the protein of Haematococcus pluvialis increased first and then decreased, while the emulsification stability showed the opposite trend. With the increase of NaCl concentration, the foam capability, foam stability, emulsion capability and emulsification stability of the protein of Haematococcus pluvialis increased first and then decreased, while the solubility showed a trend of first decreasing, then increasing, and then decreasing again.