To reduce water loss in sandy soil and enhance coastal ecosystem, this study aims to explore the effect of XG combined with MICP on the water retention of quartz sand-calcium carbonate mixed sand. Water retention tests, volume change tests, shear wave velocity tests, and microscopic analysis tests were conducted on mixed sands treated with different concentrations of XG and MICP. Results showed that compared to untreated sand, the mass loss rate of mixed soil with XG and MICP added significantly decreased. Mixed soil treated with XG-MICP combination exhibited even smaller mass loss rate. Initially, the volume change rate of XG-cured soil was high, but significantly reduced in XG-MICP-cured soil. With increasing XG concentration, the shear wave velocity of XG-cured sand decreased, while XG-MICP-cured sand showed less variation in shear wave velocity influenced by moisture content. Calcites were observed in the pores of XG-MICP samples. This experiment validates the feasibility of using XG combined with MICP to improve water retention of mixed sandy soil, offering new insights and methods for agricultural production, soil improvement, and ecological restoration in coastal areas.