A powertrain for an electric vehicle includes: a planetary gear having a first rotating element, a second rotating element, and a third rotating element, wherein a first rotating element is connected to a first shaft and the second rotating element is connected to a second shaft; a first motor configured to selectively supply power to the first shaft at two or more gear ratios; a first shift assembly configured to transfer power of the first motor to the first shaft through one of two or more external engagement gear trains having different gear ratios; and a second motor configured to selectively supply power to the first shaft and the second shaft. The third shaft is fixedly disposed on a transmission housing, and any two shafts among the first, second and third shafts restrain each other.