The three biographies of Emperor Wu of Han Dynasty, namely The Story of Emperor Wu, Dong Ming Ji and Biography of Emperor Wu, mainly record some absurd pursuits of Taoism to highlight Emperor Wu's interest in the immortal. However, the image of Emperor Wu presented in the absurd way has an obvious fictional quality, which is rather far from reality. This specific way of writing biographies has a typical meaning in the non-official biographies of Han, Wei and the Six Dynasties because it leads to the fictionalization of these non-official biographies, provides the conditions for the birth of Tang Dynasty's legends, and ultimately contributes to the rise of legendary novels. A survey of the strategies of biography writing in Han, Wei and the Six Dynasties will further our understanding of their fictional feature and the evolvement of legendary novels in Tang Dynasty.