The three-dimensional time domain parabolic equation (3D-TDPE) is derived to simulate the EM pulse propagation in straight, curved tunnels. Then the finite differential (FD) method is applied to accurately and flexibly describe the fine structures in the tunnel, such as cars. By using the alternating direction implicit (ADI) scheme to the spatial unknowns, the TDPE can be solved line by line in each transverse plane at any time step. More specifically, the computational efficiency can be improved significantly since a three-dimensional problem is changed into several one-dimensional problems. Moreover, both the Dirichlet and Neumann boundary conditions are used to estimate the transmission loss in tunnels. The rigorous numerical method, finite difference time domain (FDTD), is applied to verify the accuracy and efficiency of the proposed method. Numerical results are given to demonstrate that the proposed 3D-ADI-TDPE method can be used as an efficient tool to predict EM pulse propagation in tunnels including fine barriers.INDEX TERMS Time domain parabolic equation, electromagnetic pulse propagating, alternating direction implicit, finite differential method.