A system for biological nitrogen removal and negative carbon discharge from wastewater with low carbon-to-nitrogen ratio may include a water intake pump, a carbon capture apparatus, a carbon recovery sedimentation tank, an integrated ammonium apparatus, an autotrophic denitrification apparatus and a denitrification sedimentation tank that are connected in sequence by pipes. The carbon capture apparatus may include an anode chamber communicated with the water intake pump via a water inlet pipe and a cathode chamber communicated with the carbon recovery sedimentation tank via a first water outlet pipe. The anode and cathode chambers may be spaced apart by an ion exchange resin membrane. The anode and cathode chambers may be provided with an anode plate and a cathode plate electrically connected to positive and negative electrodes of a power source, respectively. A bottom of the cathode chamber may be provided with aerators connected to a first air compressor by a pipe.