The invention discloses a backward construction method for a prefabricated guardrail. The backward construction method for the prefabricated guardrail comprises the following steps that a processing template is manufactured; and the processing template is installed; a plurality of well-bound guardrail steel bars are clamped in the processing template, concrete is poured in the processing template, after pouring is completed, the part, protruding out of the processing template, of an inner hollow pipeline is cut, a hoisting hole for installing is formed, the processing template is dismantled, and the well-prefabricated guardrail is obtained. According to the backward construction method for the prefabricated guardrail, the concrete guardrail can be rapidly and safely hoisted away from a prefabricated area, when the prefabricated guardrail is installed, suspenders do not need to be buried in the concrete, operation is easy, the efficiency is high, the construction efficiency and quality are effectively improved, and the backward construction method for the prefabricated guardrail has pretty good market application prospects.