The invention relates to the technical field of traffic engineering, and provides a bridge guardrail prefabricating unit, a bridge guardrail construction method and a bridge. The bridge guardrail prefabricating unit comprises a guardrail wall and a pre-embedded part pre-embedded in the guardrail wall; the inner side of the guardrail wall is in an internal-sunken shape; and the pre-embedded part extends out of the bottom of the guardrail wall and is used for being mounted in a mounting hole reserved in a bridge deck in an inserted mode. Compared with a traditional cast-in-place guardrail structure, the bridge guardrail prefabricating unit can be pre-manufactured in other sites while the bridge is constructed, after the bridge deck is constructed, the bridge guardrail prefabricating unit isdirectly carried and mounted in the mounting hole reserved in the bridge deck through the pre-embedded part, the situation that the time is consumed for waiting for drying, hard and curing work of poured concrete is not needed while the dust flying situation on a construction site is reduced, and the construction period of a bridge guardrail is effectively shortened.