The invention discloses a construction method for a protective side slope. The method comprises the steps that 1, the position of an upper soil layer to be excavated is determined on an upper operation face of a base body, and an upper reinforcing body extending into the base body is arranged at the end of the upper soil layer to be excavated; 2, the upper soil layer to be excavated is excavated for forming a lower operation face, and the bottom end of the upper reinforcing body is lower than the lower operation face; 3, a lower reinforcing body extending into the base body is arranged on the lower operation face in the manner of making contact with the upper reinforcing body, and a lower soil layer to be excavated is formed on the soil body corresponding to the lower operation face; and 4, the second and third steps are executed repeatedly till soil excavation is completed, the multiple reinforcing bodies which are in contact form a side slope protective body, and the exposed faces of the multiple reinforcing bodies form the protective face of the side slope protective body.