Parallel multilevel fast multipole algorithm for scattering analysis of conducting targets situated in a half-space environment is presented. Due to the introducing of image sources to deal with the effects of the far interface interactions, the communication traffic among processes is nearly doubled compared with the free space case, which is a great challenge for designing the parallel algorithm. To achieve high parallel efficiency when using hundreds of CPU cores, the adaptive direction partition strategy is improved in this paper. The correctness is demonstrated by using a conducting sphere above ground. In addition, a real-life vehicle above ground is simulated using the proposed method and the parallel efficiency is tested.