As electron transportation in vacuum convolute structure plays a quite important role during current converging process on pulsed power facility, fully three-dimensional (3D) particle-in-cell (PIC) simulations are performed using NEPTUNE3D code to explore this process. Simulated region (34 cm×34 cm×18 cm) including the double post-hole convolute (DPHC) structure is modeled and calculated with the help of high-performance computing clusters. The calculated results including the distributions of magnetic field nulls, trajectory of electron transportation, electrons lost on surfaces of anode posts, and time-integrated electron energy deposition damaging around the magnetic null areas between posts and holes, agree with the experimental ones from the large-scale pulsed power facility. According to the calculations, maximum current loss (437 kA, 27%) happens at early time (about 15 ns), while the loss drops dramatically to only 0.48% (34 kA) when current peaks at 53 ns (7.12 MA), at this time the magnetic insulations of transforming lines have been fully established, which also proves that the DPHC structure has especially high efficiency on high-density current converging.