The invention relates to a reserved grouting hole connecting method of a prefabricated assembled bridge pier. The method is characterized by including following steps: 1), prefabricating a bridge pier body, arranging a connecting rebar in the bridge pier body during prefabricating, reserving an extending-out portion on the connecting rebar, and fixing an expanding head at the bottom of the connecting rebar; 2), casting in place or prefabricating a bearing platform in a factory; 3), forming a grout outlet, a grout inlet and a reserved grouting hole with concrete hole walls in the bearing platform; 4), hoisting the bridge pier body to space above the bearing platform, and enabling the connecting rebar extending out of the bridge pier body and the expanding head to be inserted into the reserved grouting hole of the bearing platform; 5), injecting a grouting material from the grout inlet of the bearing platform, constantly repeating the grouting process until grout is full to complete connection of the prefabricated assembled bridge pier. In the connecting method, the reserved hole and the connecting rebar are simple to dock, the grouting material is excellent in binding performance, construction speed is high, and connecting reliability is high, and the technical problems that common connecting methods are high in requirements on construction accuracy and technology, a sleeve at a joint is large in rigidity effect and a grouting sleeve or a metal corrugated pipe are prone to rusting are solved.