Research conclusions：The experiment done in the experimental section shows the compacting factor of soft rock filling material in red rock area shall be more than 0.93, and the tracks should be laid at least 6 months later after the embankment is filled. In this way, the post-construction settlement of top layer of the embankment of dig jet mixing pile composite foundation can meet requirement of the designed control standard, namely, the settlement is 15 cm and the settlement rate is 4 cm annually. The experiment also shows application of the dig jet mixing pile composite foundation with the distance between piles of 1.0 m and pile diameter of 50 cm and soft rock filling embankment is feasible, which is very significant to guiding the design and construction.