The extraction of protein from garlic processing wastewater by the membrane filtration and acid precipitation was optimized and the molecular weight， amino acid composition， isoelectric point and other physicochemical properties of the protein were also investigated. The results showed that the molecular weight of protein in garlic processing wastewater was mainly above 30 ku， so the purity of 72.11% protein was obtained from garlic wastewater by using 30 ku membrane. The molecular weight of the obtained protein was 31.9 ku and 48.4 ku， which contained seven essential amino acids. Methionine was the first limiting amino acid of the protein. The isoelectric point of the protein was approximately 3.86. DSC analysis confirmed that denaturation temperature of the protein was 73.2 ℃， and denaturation enthalpy ΔH was 11.87 J/g. At the appropriate pH， it had good solubility， emulsifying capacity， emulsion stability， foam capacity and foam stability.