Sandy　desertification　currently　poses　a　severe　environmental　challenge,　hindering　the　socio-economic　development　of　Belt　and　Road　Initiative　(BRI)　drylands.　However,　due　to　incomplete　evaluation　systems　and　unclear　driving　mechanisms,　research　on　sandy　desertification　in　the　BRI　drylands　remains　limited.　To　address　this　issue,　this　study　followed　the　Land　Degradation　Neutrality　(LDN)　framework　and　constructed　a　new　index,　called　sandy　desertification　assessment　index　(SDAI).　Based　on　SDAI,　this　study　assessed　the　status,　evolution,　and　driving　mechanisms　of　sandy　desertification　during　2000-2020.　The　findings　are　as　follows:　(1)　The　year　2006　was　identified　as　the　turning　point　for　light　and　moderate　sandy　desertification　land,　whereafter　the　areas　of　light　sandy　desertification　increased　while　the　areas　of　moderate　sandy　desertification　decreased.　(2)　The　transformation　patterns　of　sandy　desertification　levels　were　similar　in　two　decades　(i.e.,　2000-2010　and　2010-2020),　with　slight　differences　in　conversion　areas.　(3)　The　changing　trends　exhibit　regional　variability.　Notably,　reversal　was　predominantly　observed　in　China,　Mongolia,　and　India,　whereas　intensification　was　concentrated　in　Central　Asia.　(4)　Various　factors　exerted　differing　influences　on　sandy　desertification,　with　annual　cumulative　precipitation,　human　footprint,　and　gross　domestic　product　(GDP)　being　particularly　significant.　This　study　will　provide　crucial　guidance　for　formulating　prevention　and　control　strategies　in　the　BRI　drylands.