The invention relates to an electric steering engine used in a flat space. The electric steering engine comprises a main shell, an upper shell and a side end cover, wherein the upper shell is arrangedon the upper part of the main shell, and the side end cover is fixed to the side end of the main shell. The electric steering engine used in a flat space has the advantages that a rocker arm of an output shaft is long, the stress of a ball screw pair is reduced, and meanwhile, the area flattening requirement of the output shaft is met; a limiting structure of a lead screw nut uses a bearing, so that the efficiency is improved, and the limiting structure is prevented from being stuck; a lead screw gear is directly machined on a lead screw and is free of mounting; and the shells are designed ina split mode, and the mounting is simple; the length of the rocker arm of the output shaft is prolonged, so that the ball screw pair and a motor do not need to be mounted in a flat area; the lead screw nut is matched with a limiting groove of the main shell by additionally arranging the bearing through the limiting structure, so that the problem of lead screw overturning caused by the overlong rocker arm of the output shaft is solved, and the transmission efficiency of the lead screw limiting part is improved, and stuck is avoided; the split type shells are simple to mount; and the development of a small-diameter potentiometer is gradually mature and reliable, and is beneficial to mounting in the flat space.