The neutral beam injection (NBI) system with 4MW beam power of 50-80 keV beam energy was designed to provide plasma heating and current drive for high performance and long pulse operation of the Experimental Advanced Superconducting Tokamak (EAST). The system is mainly composed of the Ion Source, beam line system, power supply system, control and data acquisition system and beam diagnosis system, and with them, the NBI can produce high energy charged ion beams and neutralize them to form a high energy neutral particle beam, ultimately, the high-energy neutral particles are shoot into the plasma inside fusion device. The injected particles become fast ions by charge exchange and ionizing collisions with plasma ions and electrons and trapped in the magnetic confinement region, and then their energy is shared with the target plasma by Coulomb Collisions and increases the overall plasma temperature. On the basis of the plasma density and injection beam energy, the Injection can achieve different main heating of a particle. By tangential injection in the Tokamak, neutral beams provide also momentum to the plasma and current drive, one essential feature for long pulses of burning plasmas. The EAST NBI system focuses on the heating plasma, the other functions of momentum transport and current drive are mainly used by the related plasma diagnostics systems. In combination with other heating system for EAST device, the NBI system can maintain plasma discharge with high parameters to steady state conditions, and achieve steady state highly confined plasmas on the other hand, which lay the foundation for a comprehensive study of plasma in high parameters environment under steady state conditions.