<p>Topology optimization (TO) has been extensively developed in the past decades. It has evolved from considering single candidate material to multiple candidate materials. One major issue of the multi-material TO is the assumption of perfect joint between dissimilar materials. Therefore, multi-joint TO (MJTO) was developed to include the behavior of both structural materials and the joint materials. However, the existing works on MJTO considering the thin joint scenario are limited. The previous MJTO works usually assume that the joint material occupies one layer of element, making the joint thickness highly dependent on the meshing technique. Such assumption will overlook the thin joint condition. In this paper, a new MJTO framework is proposed to take the actual thin joint into consideration. For the proposed MJTO framework, the dissimilar material interface orientation information is used and a sandwiched joint modeling method is adopted. As a part of the MJTO framework, a novel dissimilar material interface orientation calculation method is proposed so that the sandwiched joint’s orientation will correctly reflect the interface orientation. The proposed dissimilar material interface orientation calculation method only requires the elemental pseudo densities, simplifying its implementation. Multiple numerical studies are included to demonstrate the effectiveness of the proposed MJTO framework and the proposed dissimilar material interface orientation calculation method.</p>