The Ting Kau Bridge in Hong Kong is a cable-stayed bridge comprising two main spans and two side spans. The bridge deck is supported by three towers, an end pier and an abutment. Each of the three towers consists of a single reinforced concrete mast which reduces its section in steps, and it is strengthened by transverse cables and struts in the transverse vertical plane. The bridge deck is supported by four inclined planes of cables emanating from anchorages at the tower tops. In view of the heavy traffic on the bridge, and threats from typhoons and earthquakes originated in areas nearby, the dynamic behaviour of long-span cable-supported bridges in the region is always an important consideration both in their design and health monitoring. This paper describes the development of the 3D grid model for the structural health monitoring of the bridge. The 3D grid model is intended to form the backbone of subsequent multi-scale finite element models for bridge rating. The baseline model is built up and calibrated to match the bridge geometry and cable forces specified on the as-built drawings. The modelling of the concrete deck in the simplified grid model is an important issue as it has great effect on the lateral and torsional vibrations of the bridge. This paper examines in particular the shear lag effect on the modelling strategy.