Abstract:A novel charge-conservation method with particle zigzag-line moving is introduced and it is implemented and applied in a large-scale parallel code named NEPTUNE3D for fully electromagnetic Particle-In-Cell(PIC) simulation programmed by authors. Compared with the classical PIC method, this zigzag-line charge-conservation method does not need Boris-correction which involves large linear-equations for solving problem, so it has a better robustness. Compared with other charge-conservation methods, this zigzag-line charge-conservation method does not need any judgment sentence, so its code executive efficiency is higher and it is suitable for massively parallel computation. Compared with the classical PIC method, two real devices are simulated and tested by using NEPTUNE3D with zigzag-line charge-conservation method, one is the entire high power microwave tube including magnetic transmission line oscillator and antenna, the other one is a terahertz folded waveguide travelling-wave-tube. The zigzag-line charge-conservation method simulation results are correct and agree with the classical PIC method well. Moreover, as computation duration being shortened notablely, device-design and simulation efficiency could be boosted obviously by using this new zigzag-line charge-conservation method.