The combination of Network-on-Chips (NoCs) and 3D IC technology, 3D NoCs, has been proven to be able to achieve a great improvement in both network performance and power consumption compared to 2D NoCs. In the traditional 3D NoC, all routers are vertically connected. Due to the large overhead of Through-Silicon-Via (TSV, e.g., low fabrication yield and the occupied silicon area), the partially connected 3D NoC has emerged. The assignment method determines the traffic loads of the vertical links (elevators), thus has a great impact on 3D-NoCs' performance. In this paper, we propose a congestion-aware dynamic elevator assignment (CDA) scheme, which takes both the distance factors and network congestion information into account. Experiments show that the performance of the proposed CDA scheme is improved by 67% to 87% compared to the random selection scheme, 8% to 25% compared to SelByDis-1, and 13% to 18% compared to SelByDis-2.