The isothermal synthesis method is used to investigate the vapor-liquid equilibrium (VLE) data of the ammonia (NH3) + water (H2O) + ionic liquid (IL) ternary system at the temperature of 313.15 K and the pressure of (0 to 0.6) MPa. The 3 ILs are 1,3-dimethylimidazolium tetrafluorobrorate ([Dmim]BF4), 1,3-dimethylimidazolium chloride ([Dmim]Cl) and 1,3-dimethylimidazolium dimethyl phosphate ([Dmim]DMP), respectively, and the ratio of mass (r(m)) of IL/H2O is 3/4. In addition, the densities of the three binary systems, namely, the H2O + [Dmim]DMP (r(m) = 1/2, 3/4) at 293.15 K, 313.15 K, and 333.15 K, the H2O + [Dmim]Cl (r(m) = 3/4) and H2O + [Dmim]DMP (r(m) = 3/4) at 313.15 K have been measured at atmospheric pressure, respectively. The VLE of the NH3 + H2O + [Dmim]DMP ternary system (r(m) = 1/2, 3/4) are measured at 293.15 K, 313.15 K, and 333.15 K with the pressures ranging from (0 to 0.6) MPa. Finally, an analytical polynomial equation is used to fit the experimental data.