Tidal energy, a clean, predictable and reliable renewable energy source, can play an important role in creating a carbon-free energy system in Europe. The cumulative tidal stream technology deployed in Europe was 27.9 MW in 2020, which contributes to 77% of the global total tidal energy device installations. Under a high growth scenario, about 2388 MW of tidal energy capacities will be deployed in Europe by 2030. The structural performance of a tidal turbine blade is vital as it guarantees the safe operation of a turbine within its lifespan in marine environments. Experimental testing is a reliable way of investigating the structural performance of a tidal turbine blade. In this research, the structural performance of a composite demonstrator is carried out. The 5-m long demonstrator represents a tidal current turbine’s spar cap, the strongest region of a typical rotor blade. The demonstrator consists of two spar cap and two webs, which are manufactured with glass-fibre reinforced composite materials. Steel inserts are drilled into the root of the spar cap to connect to the support frame. A hydraulic actuator is used to apply loading to the tip region of the demonstrator to simulate the operation loading. Instrumentations, including strain gauges, accelerometers and displacement transducers, are installed to monitor the demonstrator responses. Besides testing the demonstrator, the mechanical properties of the glass-fibre reinforced composite material are also obtained through coupon tests. The test results are utilised to develop a finite element model, which will be used in the blade design and optimisation case study in the future.