The theoretical analysis of emergence mechanism and linear unmixing model of mixed pixel was presented. A novel compact field hyperspectral imaging system was setup, and high accurate spectrum of endmembers was collected directly. Based on these endmembers, the model of linear unmixing of the mixed pixels was studied. The weighted spectrum obtained with the model for endmember with different abundance in the whole non-three-dimensional space was compared with the practical mixing spectrum. The accuracy of the model was verified.