Construction quality, durability and service life of China Railway Track System Ⅲ (CRTS Ⅲ) is influenced by working performance of self-compacting concrete (SCC) for filling layer. In this paper, the effect of unit water consumption, sand ratio and water reducer components on working performance of SCC filling layer was studied by laboratory and field tests. Appropriate mix proportion parameters were obtained. Results shown that unit water consumption can significantly improve the working performance of SCC, but it is necessary to comprehensively consider the dosage of water reducing agent and unit water consumption to ensure its stability. Sand ratio of SCC in the filling layer is between 49% and 52%, which can have excellent flowability and stability. It is recommended that the content of the defoamer should be 3/1 000, and the content of the air-entraining agent should be 5/1000. These research results will play an important role in improving the construction quality of SCC filling layer.