介绍了自主编制的3维全电磁粒子模拟大规模并行程序NEPTUNE的基本情况。该程序具备对多种典型高功率微波源器件的3维模拟能力，可以在数百乃至上千个CPU上稳定运行。该程序使用时域有限差分(FDTD)方法更新计算电磁场，采用Buneman-Boris算法更新粒子运动状态，运用质点网格法(PIC)处理粒子与电磁场的耦合关系，最后利用Boris方法求解泊松方程对电场散度进行修正，以确保计算精度。该程序初步具备复杂几何结构建模能力，可以对典型高功率微波器件中常见的一些复杂结构，如任意边界形状的轴对称几何体、正交投影面几何体，慢波结构、耦合孔洞、金属线和曲面薄膜等进行几何建模。该程序将理想导体边界、外加波边界、粒子发射与吸收边界及完全匹配层边界等物理边界应用于几何边界上，实现了数值计算的封闭求解。最后以算例的形式，介绍了使用NEPTUNE程序对磁绝缘线振荡器、相对论返波管、虚阴极振荡器及相对论速调管等典型高功率微波源器件进行的模拟计算情况，验证了模拟计算结果的可靠性，同时给出了并行效率的分布情况。

A massively parallel code named NEPTUNE for 3D fully electromagnetic and particle-in-cell(PIC) simulations is introduced, which can run on the Linux system with hundreds or even thousands of CPUs. NEPTUNE is capable of three-dimensional simulation of various typical high power microwave(HPM) devices. In NEPTUNE code, electromagnetic fields are updated by using finite-difference time-domain(FDTD) method to solve Maxwell equations and particles are moved by using Buneman-Boris method to solve the relativistic Newton-Lorentz equation. The electromagnetic fields and particles are coupled by using linear weighing interpolation PIC method, and the electric field components are corrected by using Boris method to solve the Poisson equation in order to ensure charge-conservation. NEPTUNE code can construct many complicated geometric structures, such as arbitrary axial-symmetric structures, plane transforming structures, slow-wave structures, coupling holes, and foils. The boundary conditions used in NEPTUNE code are briefly introduced, including perfectly electric conductor boundary, external wave boundary, and particle boundary. Finally, some typical HPM devices are simulated and tested by using NEPTUNE code, including magnetically insulated line oscillator, relativistic backward wave oscillator, virtual cathode oscilator, and relativistic klystron amplifier. The simulation results are presented with correct and credible physical images, and the parallel efficiencies are also given.