An improved algorithm for water body area extraction based on pixel unmixing is proposed in order to reduce the impact of water body boundary pixels on water body area extraction. A fraction image of water abundance was obtained with the linear pixel unmixing model using ALOS data. The threshold method and the mathematical morphology method were used to extract pure water and water body boundary pixels. Through analysis of the composition of water body boundary pixels, an area correction algorithm for water body boundary pixels is proposed to correct the water body area. The research results show that, compared with the linear pixel unmixing model, the proposed method can improve the accuracy of water body area extraction by 6. 7% at most, and can reduce the impact of the water content of washlands on the calculation of water abundance of water body boundary pixels.