Firstly， whey protein isolate (WPI) was hydrolyzed by trypsin at constant conditions (i.e.， pH 8.5， 37 °C， enzyme/substrate ratio: 0.5%， 5 h) to prepare whey protein hydrolysates (WPH). Secondly， this study evaluated the influence of milieu conditions on emulsifying properties of WPH. Namely， pH values (3-7) and ionic strength (0.1 mol/L and 1 mol/L) by means of the addition with different salts (NaCl， KCl， CaCl2， MgCl2) were combined with heat treatment of WPH prior emulsification. For emulsion characterization， particle size distributions were measured by laser diffraction， emulsion stability was evaluated by STEP technique， and mass spectrometry was used to identify individual precipitated peptides due to heat treatment or the changes of milieu conditions. It was found that the charge-shielding effect caused by the increase in ionic strength at pH3 led to significant emulsion flocculation， while the effect of ionic strength on the emulsification characteristics of WPH at pH7 was insignificant. In addition， at the isoelectric point of WPH (pH4)， heat treatment significantly improved the emulsification characteristics of WPH， especially for the sample group with the addition of CaCl2. Combining the composition of the precipitated peptides at different environmental conditions and the corresponding emulsification characteristics， f(41-60)， f(71-91)， and f(78-101) released from β-Lg are believed to make an important contribution to the emulsification characteristics of WPH.