The present invention relates to a powertrain for an automatic transmission. The powertrain for an automatic transmission consisting of an input shaft, an output shaft and first to third planetary gear sets comprises: first to seventh actuating elements constituting the first to third planetary gear sets; and shifting elements including first to fourth clutches and first and second brakes, wherein at least two of the shifting elements are actuated so that the first to seventh actuating elements are driven or restrained, thereby implementing eight forward speed and two reverse speed ratios.