A retaining wall structure includes a number of bag units piled to form a wall and interconnecting units disposed between vertically adjacent bag units. The interconnecting units each has a plate and protrusions protruding from upper and lower surfaces of the plate. A reinforcing layer is provided between the plate of a relative interconnecting unit and a relative bag unit. The reinforcing layer is selected from cement or adhesive (such as glue). The present invention uses the reinforcing layer between the plate of the interconnecting unit and the bag unit to enhance the entire stability of the retaining wall adapted for operation in different circumstances.