The invention relates to a tall retaining structure of a weak geological slope. The tall retaining structure comprises pile foundations, stand columns, a bottom plate main beam, rib plates, bottom plate connecting plates, inter-column soil retaining plates, a crown beam, a connecting beam and a connecting beam anchor. A pile plate wall structure composed of the stand columns and the inter-column soil retaining plates is located on the upper part of the retaining structure, a counterfort retaining wall structure is composed of the stand columns, the inter-column soil retaining plates, the bottom plate main beam, the bottom plate connecting plates and the rib plates, and the pile foundations are located on the lower part of the retaining structure, penetrate through a weak soil layer and enter a hard rock layer to provide stable supporting; the upper ends of the stand columns are horizontally connected into a whole through the crown beam, stability of the whole structure is ensured, andthe connecting beam and the connecting beam anchor arranged in the hard rock layer pull the stand columns laterally to prevent the stand columns from laterally moving or collapsing. The retaining structure has high adaptability in complex mountain terrains, is especially suitable for weak geological conditions, and is safe and reliable in structure; the support height is higher than that of existing support structures, great convenience is provided for mountain engineering construction, and the retaining structure has high popularization and application value in the field of slope protection.