Abstract: The fully-electromagnetic particle-in-cell method can accurately simulate the nonlinear interaction between strong electromagnetic field and electron beam, this method is widely adopted in the design and parameter optimization in the vacuum electronic devices (VEDs). Traditional fully electromagnetic particle-in-cell method uses the finite-difference time-domain (FDTD) method to simulate electromagnetic wave in the device. The classical FDTD method uses the structured grid, which will bring the stair-cased error. The finite element method adopts the unstructured grid to accurately describe the complex model and can be used to simulate the electromagnetic field in complex structure, since this method needs to solve large inverse matrix, it is very difficult to employ this method to simulate large-scale structures. In order to accurately simulate the nonlinear interaction between electromagnetic field and electron beam in complex VEDs, researchers have made breakthrough in the field of conformal electromagnetic particle-in-cell (CEMPIC) method. The fully electromagnetic particle-in-cell method based on conformal FDTD method is realized, meantime, the electromagnetic particle-in-cell method based on finite-element time-domain (FETD) method is also proposed, and the numerical simulation codes are developed. To promote the research and application of CEMPIC for complex structures in China, firstly, the key techniques in the study of particle-in-cell method based on FDTD method for complex structures are introduced in this paper in details, including the conformal structured grid generation, conformal FDTD method, conformal electron beam emission. Secondly, the particle-in-cell method based on FETD method is also presented, the key technology including primary function, charge conservation and divergence-cleaning algorithms developed in the finite-element particle-in-cell (FEMPIC) is also unveiled. Finally, the typical simulation results for typical VEDs by using the two simulation technologies are also presented.