Abstract: In order to obtain self-consistent space charge limited electron emission model in electromagnetic PIC(particleincell) simulation of foilless diode, Child law model, Gauss law model and 1D diode model have been analyzed and compared. The simulation results show that the three models are all selfconsistent with electromagnetic field. Gauss law model tends to be affected by the width of the first cell and yield nonphysical oscillation. 1D diode model with reasonable discrete grid gets almost the same results as Child law model, but it needs to solve a transcendental equation, which would cost much time. And it is demonstrated that the external applied magnetic field has little influence on the emission model and can be neglected in the electromagnetic PIC simulations. Child law mod