A piston of a gasoline direct engine may include a protuberance portion protruding along a circular arc shape having a radius (R1) equal to the piston diameter to have a predetermined height (T) from the upper surface thereof, and the edge of the protuberance portion is rounded to be connected with the upper surface; a bowl (B) having a bottom surface (F1) having an asymmetrical ellipse shape from the center of the protuberance portion to the intake side direction thereof, wherein the bottom surface thereof becomes deeper in the exhaust side direction to have a predetermined slope angle (θ1), and the inner wall portion thereof has a circular arc shape to form a predetermined rising angle (θ2) at the upper part thereof; and trumpet portions (TR) of which edge ends (E) thereof are expanded in the intake side direction of the protuberance portion to be connected to the bowl (B).