A block unit for repairing flow passage facilities is provided for permitting a desired repair operation. A method of repairing flow passage facilities using the block unit is also provided. The block unit includes an inner plate defining an inner surface, an outer plate disposed along a peripheral edge of the inner plate, and a plurality of reinforcing ribs for reinforcing the inner plate and the outer plate. The block units adjoining in a circumferential direction are joined together with bolts inserted through both circumferential end faces of each the block unit and nuts fitted on the bolts to form a short tube within a flow passage. The short tubes are connected in a longitudinal direction to form a continuous tubular assembly having an outer diameter smaller than an inner diameter of the flow passage. A grout material is injected into a clearance space formed between the tubular assembly and the flow passage.