We determined the boundary of Siertan Wetland at Yanchi County in Ningxia using the polar ordination method, and investigated the biodiversity of the study area. Along the biotope gradient from wetland to grassland, the ectone could be divided into the quadrats N8 - N13 in the north transect line, quadrats S15 - S24 in the south transect line, quadrats E13 - E22 in the east transect line , and quadrats W23 - W30 in the west transect line; The diversity index and richness index of the four transect lines all followed the order of ectone > arid region > wet region, the evenness index ordered as arid region > ectone > wet region, and the dominant concentration index ranked as wet region > ectone > arid region. Affected by human disturbance and topographical difference, the plant communities varied in different directions, and the richness index, diversity index and evenness index of the north and east transect lines were higher, while the dominant concentration index was lower.