Abstract: Pressure-balanced water tank is applied to balance the water pressure in concrete volute at a hydroelectric power station which has operated safely for decades. However， corrosion occurred in the tanks in these years. It is too difficult to repair and there is a safety problem in the power station. In order to study the feasibility of backfilling micro-expansion SCC as substitution for pressure water， experiments of preparation and performance have been carried out according to the design requirements. By adopting the site raw materials， mix parameters such as water-cement ratio and sand rate are determined by a series of fresh concrete tests and strength tests. The relationships between the dosage of swelling agent and deformation of concrete have been studied by restricted expansion experiments， autogenous volume deformation tests and uniaxial expansion experiments. The filling ability of this type of SCC is verified by rheological experiments and a simulative self-filling test. The mix proportion and the performance of backfilling micro-expansion SCC can provide a reference for relative researches and similar works of hydraulic engineering.