The utility model discloses a karst formation pile hole wall protection structure, aiming to effectively strengthen the stability of the hole wall and improve the construction efficiency of a diggingpile. A pile hole is composed of pile hole segments (10) which are dug in section, the hole wall of the pile hole segment (10) is fixedly provided with a block steel moulding plate (22) to form a sealcoat, the surface of the block steel moulding plate (22) is provided with preformed holes which are distributed in intervals on the circumferential direction and the longitudinal direction, squeezingholes (12) are drilled from the performed holes towards an unstable karst unconsolidated formation (11), grouting pipes (21) are installed in the squeezing holes (12), and grout which is filled through the grouting pipes (21) can integrally consolidate the unstable karst unconsolidated formation (11) after diffusing and solidifying.