<p>Inland saline–alkaline wetlands are highly heterogeneous and dynamic ecosystems in which habitat contrasts and hydrological variation shape biodiversity patterns. Aquatic insects are key components of wetland ecosystems and sensitive indicators of environmental change. However, how habitat heterogeneity and hydrological periods jointly regulate their multidimensional diversity remains poorly understood. Here, we examined taxonomic and functional α- and β-diversity of aquatic insect communities across two habitat types (macrophyte-dominated and open-water wetlands) and two hydrological periods (normal and flood) in inland saline–alkaline wetlands of the western Songnen Plain, Northeast China. Community composition differed between habitat types and hydrological periods, with macrophyte-dominated wetlands consistently supporting higher taxonomic α-diversity and functional richness than open-water wetlands. Taxonomic and functional β-diversity varied markedly among habitat–period combinations. Turnover dominated in open-water wetlands, whereas macrophyte-dominated wetlands showed relatively greater nestedness and stronger temporal shifts, especially during the flood period. Moreover, aquatic insect diversity patterns and their relationships with environmental variation were strongly dependent on the interaction between hydrological period and habitat type. Overall, habitat heterogeneity and hydrological period jointly shaped aquatic insect diversity in inland saline–alkaline wetlands, with habitat heterogeneity exerting the stronger baseline influence. These findings highlight the value of integrating taxonomic and functional perspectives for biodiversity assessment and wetland management.</p>