Carbon nanotubes(CNTs)have been proven experimentally to be well suited for field emission applications.However,the exact process of electron emission from CNTs is still not fully understood.In this paper,we numerically investigate the effects of electrostatic field screening at the CNT emitter tips by finite element method and show the impact on device performance.We further observe that to achieve maximum emission efficiency of CNTs in an infinite line,one need to have an intertube distance of three times the CNT height.