Abstract: The runoff in northwest China is seriously polluted by nitrogen, phosphorus and pathogenic microorganisms, posing a threat to the ecosystem. Due to the limited economic conditions in the region, there is an urgent need to build bioretention facilities that are both efficient and cost-effective to achieve sustainable pollution control. A rainwater retention column with a functional stratified medium structure was developed using corn stalk biochar. The upper layer was a mixed medium of corn stalk biochar and sand (volume ratio of 25%), and the lower layer was an iron-modified corn stalk biochar functional layer. The column experiment results showed that this stratified medium structure could synergistically remove various pollutants: the upper layer medium significantly improved the capacity for ammonia nitrogen （\mathrmNH_4^+ -N） removal and hydraulic performance; the lower layer iron-modified corn stalk biochar functional layer had high removal efficiency for phosphate （\mathrmPO_4^3- -P） and Escherichia coli in the runoff. The adsorption of \mathrmPO_4^3- -P by iron-modified corn stalk biochar conformed to the pseudo-second-order model (R²>0.99), and the adsorption isotherm curve followed the Langmuir model (R²>0.97). The modified surface structure of iron-based biochar was further analyzed through scanning electron microscopy, Fourier transform infrared spectroscopy and nitrogen adsorption-desorption isotherms. In conclusion, this stratified medium design, through functional zoning, not only effectively controls nutrient pollutants and pathogenic bacteria in the runoff but also offers significant cost advantages, providing a sustainable solution for rainwater management in arid and economically underdeveloped areas of Northwest China.