The　traditional　finite-difference　time-domain　(FDTD)　method　is　constrained　by　the　Courant-Friedrich-Levy　condition　and　suffers　from　the　notorious　staircase　error　in　electromagnetic　simulations.　This　article　proposes　a　3-D　conformal　locally　one-dimensional　FDTD　(CLOD-FDTD)　method　to　address　the　two　issues　for　modeling　perfectly　electrical　conducting　(PEC)　objects.　By　considering　the　partially　filled　cells,　the　proposed　CLOD-FDTD　method　can　significantly　improve　the　accuracy　compared　with　the　traditional　locally　one-dimensional　FDTD　(LOD-FDTD)　method　and　the　FDTD　method.　At　the　same　time,　the　proposed　method　preserves　unconditional　stability,　which　is　analyzed　and　numerically　validated　using　the　von　Neumann　method.　Significant　gains　in　central　processing　unit　time　are　achieved　by　using　large　time　steps　without　sacrificing　accuracy.　Two　numerical　examples,　including　a　PEC　cylinder　and　a　missile,　are　used　to　verify　its　accuracy　and　efficiency　with　different　meshes　and　time　steps.　It　can　be　found　from　these　examples　that　the　CLOD-FDTD　method　shows　better　accuracy　and　can　improve　the　efficiency　compared　with　those　of　the　traditional　FDTD　method　and　the　traditional　LOD-FDTD　method.　©　1964-2012　IEEE.