Abstract: According to the problem of rigid and restricted physical activity of the personnel protection material, two kinds of flexible composites with shear thickening fluid (STF) and silicon rubber filling warp knitted spacer fabric (WKSF) were designed, and the impact properties of composites were studied.The WKSF has the upper and lower outer layers and spacer layer, the spacer layer was composed of spacer yarns.STF and the silicon rubber were filled into the spacer layer.STF was composed of nano-SiO₂ suspended in polyethylene glycol (PEG) liquid, and silicon rubber was composed of silicone component and curing agent mixture components.The rheometrics was used to test the rheological behaviors of STF, and Instron drop tower impact tester was used to test the impact properties of the WKSF and the flexible composites.Results indicate that STF shows shear thickening transition after reaching the critical shear rate.The impact process of the pure fabric can be divided into three stages of elastic stage, plateau stage and densification stage.There is a plateau stage for the WKSF.The impact processes of the two kinds of flexible composites are different from pure fabric, the force-displacement curves are in linear way.The silicon rubber filled composites show higher stiffness and no strain rate effect.The STF filled composites show higher energy absorption capacity and obvious strain rate effect.