The invention discloses a bipolar thin film transistor device with a composite active layer and a preparation method of the bipolar thin film transistor device. A substrate, a grid, an insulation layer, an inorganic semiconductor active layer, a source, a drain and an organic semiconductor active layer sequentially form a bottom grid structure, the source and the drain form a source-drain thin film layer at the same layer, the inorganic semiconductor active layer and the organic semiconductor active layer are arranged on the two sides of the source-drain thin film layer, and thus, an inorganic-organic composite structured active layer of the bipolar thin film transistor device is formed. With full combination of the advantages of rich material, relatively high mobility and relatively simple preparation method of an inorganic N-type semiconductor and the advantages of various material types, relatively high mobility and relatively high stability of an organic P-type semiconductor and the combination of the characteristics of a bottom grid top contact structure, the damage to an organic thin film transistor during the etching process is avoided better, and N-type and P-type outputs are achieved when the composite active layer is reasonably applied to the bipolar thin film transistor device.