Abstract: In order to reveal the effects of external admixtures on the root growth and soil consolidation and slope protection of vegetation concrete, Festuca arundinacea was used as the research material, and different contents of coconut fiber and fly ash were added to construct vegetation concrete to measure the growth characteristics of Festuca arundinacea underground root system and the shear strength of root-soil complex. The results showed that the content of coconut fiber and fly ash had significant effects on the growth of Festuca arundinacea root system. The total root length, root surface area, root average diameter and underground biomass all increased first and then decreased with the increase of the content of coconut fiber and fly ash. When the content of coconut fiber was 0.3% and the content of fly ash was 2%, they reached the maximum value, which increased by 31.39%, 30.20%, 30.57% and 12.80%, respectively, compared with the treatment without coconut fiber. Compared with the treatment without fly ash, they increased by 42.17%, 22.85%, 16.48% and 29.22%, respectively. The coconut fiber content and fly ash content also had significant effects on the shear strength of the vegetated concrete substrate. The shear strength of the substrate increased first and then decreased with the increase of the addition content, and reached the maximum value when the content of coconut fiber and fly ash was 0.3% and 2%, respectively. The comprehensive evaluation showed that the improved vegetation concrete with Festuca arundinacea root system mixed with 0.3% of coconut fiber and 2% of fly ash had the best growth, and the shear strength of vegetation concrete was the highest.