This paper describes a process to perform nanoscale welding of multi-walled carbon nanotubes (MWCNTs) using a conductive atomic force microscopy (AFM) tip. An AFM tip can be used not only to apply a mechanical force to push, drag or scratch a sample, but also to exert an electrostatic force between the conductive tip and a sample substrate by applying a bias voltage. This electrostatic field will be extremely high, due to the phenomenon of local field enhancement. Such a high electric field will provide enough energy for the metal atoms to evaporate from the conductive tip. In this paper, a model is developed to simulate the electrostatic field by adjusting the distance and the bias voltage between the conductive tip and substrate. The simulation results show that the radius of the conductive tip, the bias voltage and the gap distance will all affect the electric field intensity. In our experiments, MWCNTs are first assembled between a pair of electrodes using a dielectrophoresis (DEP) technique. Then, an electrostatic field is applied to weld MWCNTs onto the surface of microelectrodes. The experimental results show that MWCNTs can effectively be welded and the electronics performance can also be greatly improved.