Bending instability in electrospinning jet motion is the main cause of irregular collection of nanofibers on the collector. This instability forces the jet to go on a conical solenoid like motion, and produce a magnetic field which stabilizes the jet. In this paper, ViziMag software was used to calculate the produced magnetic field through simulating jet motion and investigate some influential parameters including voltage and tip to target distance on field strength. Then, the mechanism of applying external magnetic field in magnetic field-assisted electrospinning (MFAES) was investigated based on the summation of simulated jet magnetic field lines and external magnets drawn by ViziMag software. The magnetic field produced due to electrospinning jet was too small to have any effect on jet alignment but the main cause of alignment in MFAES was collecting the charged jet exactly on the field lines of external magnets which act similar to iron fillings.