The utility model discloses a bridge reinforced concrete guardrail of prefabricated-and-cast-in-situ process construction, which is composed of a prefabricated part 1, a cast-in-situ part 2 and reserved steel bars 3 of a bridge flange plate. The prefabricated part 1 is provided with pouring holes for concreting of the cast-in-situ part and side pre-embedded members 5 and a bottom pre-embedded member 6. The cast-in-situ part 2 is provided with steel bars 7 which are colligated or welded with the side pre-embedded members 5 and the bottom pre-embedded member 6 of the prefabricated part 1 and the reserved steel bars 3 of the bridge flange plate. The cast-in-situ part 2 is poured with expansion concrete to prevent crack generation between the cast-in-situ part and the prefabricated part due to the concrete contraction. The prefabricated part 1 is provided with a through hole 8 and a groove 9. The visual effect and the quality of the prefabricated part are ensured through the fine production in factories, and each prefabricated part and the bridge flange plate are connected through the on-site pouring of the cast-in-situ part, so that the overall protection effect of the guardrail is guaranteed, on-site construction is simplified, on-site construction speed is accelerated, and construction period is shortened.