Oat protein isolate (OPI) was extracted from oat. The solubility, foaming properties, emulsifying activity and subunits properties of OPI under different pH and ionic strength were studied. The results showed that，at pH 5.0~6.0, OPI has the lowest solubility, the lowest foaming, the highest foam stability, and under alkaline conditions higher emulsification and emulsion stability. Acidic conditions of pH 2.0 and 3.0 cause partial hydrolysis of soluble OPI peptide chains, forming a subunit between 31.0 to 43.0 kDa. No significant difference was found under the alkaline conditions. The solubility was the lowest when the NaCl concentration was 0.05 mol/L, and The foaming property foam stability and emulsifying property were higher when the NaCl concentration was in the range of 0.6~0.9 mol/L. When the solubility was the lowest, the soluble protein was mainly composed of 43.0 kDa, and the addition of NaCl caused the partial hydrolysis of the soluble OPI peptide chain, forming subunits of 43.0, 66.2 kDa.