Calcium chloride (CaCl2) aqueous solution as a liquid desiccant has the disadvantage of low vapor pressure and easy crystallization. Ionic liquids (ILs) such as [Emim]Cl, [Emim]Ac, and [Emim]Br have been verified to have a good ability to reduce the vapor pressure. In this paper, the vapor pressures of four kinds of CaCl2 + ILs + H2O were measured, which were CaCl2 + [Emim]Br + H2O (mass ratio CaCl2/[Emim]Br = 2:1) at temperatures of between 311.10 and 394.45 K, CaCl2 + [Emim]Cl + H2O (mass ratio CaCl2 / [Emim] Cl = 2:1) at temperatures of between 306.58 and 393.89 K, CaCl2 + [Emim]Ac + H2O (mass ratio CaCl2/[Emim]Ac = 2:1) at temperatures of between 304.93 and 382.71 K, and CaCl2 + [Emim]NO3 + H2O (mass ratio CaCl2/[Emim]NO3 = 2:1) at temperatures of between 312.46 and 391.80 K, with the mass fraction of solute ranging from 0.2 to 0.5. The Antonie-type equation was used to fit the measured results. The average absolute relative deviation (AARD %) values of the measured vapor pressures and calculated vapor pressures were 0.52, 0.40, 0.33, and 0.27%, which showed good consistency and accuracy. Comparing the vapor pressures of the different solutions at the same concentration, the following order of the four anions with the ability to reduce the vapor pressure of CaCl2 + H2O can be drawn at a mass fraction of 0.4: Br- > Cl- > NO3- >Ac-.