Abstract: A novel kind of energy-absorbing material that is frequently utilized in protective structures is shear thickening fluid (STF)，Its attributes include ease of production and protection of the environment. STF was successfully prepared in this work. Then add the STF to the honeycomb sandwich structure to strengthen it against impacts. Low-velocity drop hammer impact experiments investigated the effects of honeycomb aperture diameter, honeycomb wall thickness, and impact velocity on honeycomb sandwich structures. The DIC method was used to determine the strain history and deflection of the structure, and investigations were carried out on the mechanism of low-velocity impact response of honeycomb sandwich panels. The results shows that there are differences in the deformation patterns of the honeycomb sandwich structure's back panel with and without STF filling. In the case of the former, the back panel's center area exhibits bump deformation, while the surrounding area displays significant bulging deformation. In contrast, the back panel with STF filling exhibits bump deformation without bulging deformation, and its localized bump area is larger. The filled STF can lessen the back panel of the structure's deformation deflection and the intrusion depth of the falling hammer in the velocity range (1 m/s–2 m/s) examined in this paper. Increasing the impact velocity is more favorable for STF to produce the thickening effect, the other side, this effect of STF is influenced by the honeycomb's aperture diameter and wall thickness. The larger aperture diameter structure is beneficial to the STF hardening effect because it increases the number of honeycomb cells involved in absorbing energy, expands the structure's local deformation region, and reduces the dimensionless deflection of the structure. On the other hand, the thick honeycomb wall mitigates the impact of the falling hammer, which is detrimental to the STF hardening effect, and the thinner honeycomb wall structure is beneficial to the STF hardening effect. The study's results serve as a certain reference for the application of STF in protective structures. Future research will concentrate on examining the coupling mechanism between STF and protective structures as well as the design techniques that allow the structure under consideration to be lighter.