Reed is one of the important community types in wetland ecosystems, and its aboveground biomass (AGB) is a key index characterizing the quality of these ecosystems. In this study, the spatial distribution of reed wetland in the Western Songnen Plain was mapped using the object-oriented classification method combined with multi-seasonal Landsat8 OLI remote sensing data. Field observed reed aboveground biomass data and five spectral vegetation indices, i.e., normalized differential vegetation index (NDVI), ratio vegetation index (RVI), enhanced vegetation index (EVI), modified soil adjusted vegetation index (MSAVI), and weighted difference vegetation index (WDVI), which were derived from moderate-resolution imaging spectroradiometer (MODIS) products, were used to determine the sensitivity of different spectral vegetation indices to reed AGB and further to develop an optimal remote sensing model for reed AGB estimation and inversion. The results showed that, the total area of reeds in 2014 was 1653 km² in the Western Songnen Plain, and Zhalong Wetland Nature Reserve had the largest reed area (1178 km²) among the five wetland natural reserves. Additionally, strong correlations were found between each of the five vegetation indices and reed AGB (P < 0.01). The exponential curve model established using EVI was the optimal model (R² = 0.55) for reed AGB estimation and inversion. In the Western Songnen Plain, the mean reed AGB based on the exponential curve model was estimated to be 372.1 g/m² and the total reed AGB to be 6.14×10⁵ t. The maximum reed AGB was observed in Zhalong Nature Reserve with a value of 4.38×10⁵ t. The averaged reed AGB for each of the five wetland natural reserves can be listed in a decreasing order as Xianghai Natural Reserve (469.7 g/m²) > Dabusu Natural Reserve (454.1 g/m²) > Momoge Natural Reserve (373.0 g/m²) > Zhalong Natural Reserve (372.4 g/m²) > Chagan Lake Natural Reserve (369.8 g/m²). Higher AGB values were found in the southern area than in the northern. Results from this study could contribute to the protection and management of reed wetland, and the utilization of reed resource.