Composite inserts are a well-known and innovative technology in the automotive industry used to improve safety, NVH (noise, vibration, and harshness) and fatigue life of vehicles, as well as to reduce vehicle weight and manufacturing cost. In order to study the crashworthiness performance of composite inserts in a vehicle structure, a three-point bending test of simplified steel-composite combined beam structures is considered. The beam structure in this investigation has a double-hat section. Epoxy-based structural foam and 33% short glass fibre reinforced nylon insert are considered as composite fillers for the two empty beam sections. Four cases, based on the different combination of composite materials inserted in the beam sections, are considered. The test results show that the composite insert greatly contributes to improvement of the energy absorption of beam structure. The force-displacement (F-D) curves of bending tests, the deformation behaviours of beam structures and the failure modes of composite inserts are shown and analysed to understand the effects of composite inserts to the crashworthiness of the beam structure in a bending condition. The numerical study was performed to develop a practical finite element (FE) model of the steel-composite combined structure.