In order to solve the problem of insufficient carbon source in actual sewage treatment, the biological nitrogen removal performance of modified nano-pyrite as electronic donor was explored. Natural pyrite was milled to nanometer scale, mixed with dimethyl sulfoxide solution, and then calcined at 600℃ for 2 hours without oxygen to obtain modified nanometer pyrite. XRD, SEM and BET analysis results showed that the pyrite with high crystallinity was transformed into pyrrhotite with low crystallinity (Fe0.95S1.05) through modification and showed a porous honeycomb structure. The specific surface area increased from 0.82 m2/g to 10.54 m2/g, and the pore size increased from 7.70 nm to 22.41 nm. At the same time, VSM results showed that the magnetic strength of modified nano-pyrite was 12 emu/g. The effects of different physical and chemical factors on the biological nitrogen removal performance of modified nano-pyrite were investigated. The results showed that under the experimental conditions of 500 mg/L of modified nano-pyrite, temperature 30~35℃, pH 6.5~7.5, the concentration of NO3--N in the simulated wastewater decreased from 18.5 mg/L to 0.362 mg/L, the reaction time shortened from 4.5 h to 1 h, and the removal rate of NO3--N increased from 42.8% to 98.2% compared with that before the modification, which showed that the modified nano-pyrite could be used as an electronic donor by denitrifying microorganisms efficiently. The analysis of denitrification kinetics showed that the kinetics of autotrophic denitrification (MNPAD) reaction with modified nano-pyrite as electron donor was in line with zero-order reaction characteristics (R2>0.97).