In view of the scattering calculation problem of multiple 3D conductor targets located above the rough surface, this paper proposes a hybrid AIM-PO algorithm of adaptive integral method (AIM) combined with physical optic (PO) method. In this algorithm, the scattering from rough surface is calculated by PO, and the scattering from target is calculated by AIM. The scattering from the rough surface is solved as part of the target impedance matrix, and the target the rough surface are solved as a whole. The most important computational bottleneck comes from the complement of the coupling matrix between the target and the rough surface in the process of solution. In order to overcome such a computational bottleneck, a fast multipole algorithm (MLFMA) combined with a fast far field approximation (FaFFA) algorithm is proposed to accelerate the matrix vector multiplication. The method is based on the far field approximation criterion to divide the rough surface area into near and far regions, i.e., the distance between the upper element of the rough surface and the target satisfied with the far field approximation conditions is classified as a far region, otherwise is classified as a near region. The near zone is accelerated by MLFMA, whereas the far zone is accelerated by FaFFA. Compared with the traditional numerical algorithm, the proposed algorithm has high computational accuracy, and can effectively improve the computational efficiency. Finally, the variation law of multi-target and environment composite scattering characteristics under different conditions is analyzed by numerical calculation.