Experiments of the fish-shaped and triangle phase diagrams of the water + dodecane + 1-(1-methyl-2-propoxyethoxy)-2-propanol (C3P2) system were performed under atmospheric pressure. It was found that the upper and the lower critical solution temperatures of this ternary system are, respectively., (287.20 +/- 0.05 and 275.00 +/- 0.05) K according to the fish-shaped phase diagram. Triangle phase diagrams exhibit only one two-liquid-phase-coexisting region at (288.15, 298.15, and 308.15) K, above the upper critical solution temperature. The nonrandom two-liquid (NRTL) model was used to correlate the experimental data of triangle phase diagrams at these three temperatures.