The vapor-liquid equilbria(VLE) data for a water-DMF binary system at 101.33 kPa、13.33 kPa and a Water-DMF-formic acid ternary system were measured by using an improved Roseequilibria cell. UNIQUAC,NRTL and Willson equation were used to correlate the water-DMF VLEdata.VLE data for water-DMF-formic acid system has been estimated by using Wilson equation.Theevaluation results all agreed well with experimental data.