In order to explore the potential environmental risks associated with high-volume land application of separated pig digested slurry and determine its optimal application rate, a two-year field experiment was conducted to investigate the effects of different application rates on the production performance Pennisetum purpureum and soil quality under complete substitution of chemical fertilizers with pig slurry. The study systematically analyzed the crude protein content, biomass, and heavy metal accumulation characteristics of Pennisetum purpureum, as well as soil nutrients (total nitrogen, total phosphorus, total potassium, alkali-hydrolyzable nitrogen, available phosphorus, available potassium, and soil organic matter), heavy metal content, and pH. The results showed that : pig Slurry irrigation significantly increased heavy metal content in Pennisetum purpureum, with the F4 treatment (200% of chemical N fertilizer rate) reaching the highest levels. However, all treatments remained well below the limits specified in the Hygienic Standard for Feeds (GB 13078-2017),which ensuring the forage grassfeed safety.Under the 200%N application rate, soil nitrogen, phosphorus, and organic matter content significantly increased compared to conventional chemical fertilization (except for potassium), demonstrating notable soil fertility improvement.The experimental area exhibited a naturally high background level of cadmium (Cd), and Cd accumulation was observed following slurry application. However, thecontents of the other four heavy metals(Cu, Zn,As,Hg) analyzed were than those in the Risk Control Standard for Soil Contamination of Agricultural Land(GB 15618-2018).Under the experimental conditions, high-volume pig slurry application (≤200%N) in Pennisetum purpureum cultivation systems proved feasible, maintaining yield and forage quality while enhancing soil fertility and keeping environmental risks manageable. For practical applications, it is recommended to control slurry application rates below 200%N to achieve a balance between production efficiency and ecological safety.