The UNIPIC code is used to simulate working process of a rod-pinch diode.The influences of anode plasmas and diode structural parameters on electron pinching are investigated.The electron beams don’t pinch to the rod tip at 1-2 MV without the ion effect.When the ions emitted from the anode surface reach a current of certain value

further increase of the ion current does not have a significant influence on the diode total current and the current density at the rod tip.With all the three surfaces of the cathode emitting electrons

the pinching quality of the electron beam emitted from the upstream surface is the best of all surfaces.Increasing the cathode length does not have an obvious effect in accelerating the process to achieve strong pinching.Influence of the distance from the anode tip to the cathode surface is analyzed

too.The differences between numerical simulations and experimental results are explained.