Abstract: Coral sand is widely used as a preferred building material for emergency projects of reef islands in the South China Sea. The mechanical properties of coral mortar are normally low due to the loose porosity, low particle strength and easy breakage of coral sand, making it hard to meet the requirements of practical projects. It is well recognized that graphene oxide (GO) can effectively improve the mechanical properties of coral mortar, but limited studies focus on the dynamic mechanical properties of GO-modified coral mortar under impact loads. In this study, a series of impact compression tests and microscopic tests were conducted on GO-modified coral mortar to investigate effects of GO content and strain rate on its dynamic mechanical properties and microscopic behaviors, respectively. Experimental results demonstrate that stress-strain curves of coral mortar could be approximately divided into four stages, and the development patterns of the curves were combinedly influenced by GO content and strain rate. The dynamic compressive strength of GO-modified coral mortar firstly increases and then decreases with increasing GO content, with a maximum value at 0.03wt% of GO content. Also, the dynamic strengthening factor (DIF) and toughness index of GO-modified coral mortar show obvious strain-rate effects. Microstructural observations imply that the addition of GO could drive hydration products to fill the cracks or large pores inside coral mortar, leading to improvements in its structural integrity and impact resistance performance.