With the development of marine industry, coastal sand and soil water retention has become an important technical link in the ecological recovery of islands and reefs. The effect of synergising xanthan gum (XG) with Microbially Induced Calcium Precipitation (MICP) on the water retention properties of silica sand-calcium carbonate mixed sand was investigated by treating the sand with both XG and MICP simultaneously. A series of experiments including water retention, volume change, shear wave velocity and microscopic analysis were carried out to evaluate the treated sand at different concentrations of XG and MICP. The results showed that the water storage characteristics of the cured soil improved significantly with increasing xanthan gum content and MICP concentration. Compared with the untreated sandy soil that produced a mass loss rate of 72.59% over 7 d, the mass loss rate of 5% 2.0 XG-MICP cured soil was only 13.1%, which was reduced by a factor of about 81.95%. The rate of change in volume of the XG-MICP cured soil over the 7 d test days was less than that of the XG cured soil, and the XG-MICP cured soil had a higher volumetric stability. With the increase of xanthan gum concentration, the shear wave transmission time of XG-cured soil was prolonged and the shear wave velocity decreased. Compared with XG-cured soil, XG-MICP-cured soil showed greater shear wave transmission time and smaller shear wave velocity as affected by moisture content. The pores of XG-MICP samples showed rhombic calcite precipitation. The experiment verified the feasibility of using xanthan gum combined with MICP technique to improve the water storage of mixed sandy soils, which is expected to provide a reference for improvement of sandy soils in coastal areas.