In the history of Chinese calligraphy, Zhang Xu is not only famous for his strange cursive style and considered to be a reformer, but also a key person of transmission of traditional calligraphic technique into next generation. This means that Zhang Xu or his successors wrote down and disclosed the secret of the technique so that they could easily access to the secret and freely exploit it. Along with this reformation, the background thoughts of calligraphy shifted from Taoism to Zen Buddhism. From the middle Tang era onwards, they began to emphasise the experience of self-awakening more and more. Zen Buddhism also insists that only who have experienced self-awakening can transmit the dharma. This shows a kinship between theories of calligraphy and Zen Buddhism.