This is a classical piano tune that is masterfully transcribed (by arranger Wang Jianzhong 王建中). In English, it is also called “Colourful Clouds Chasing the Moon”. In Chinese, it is called 彩云追月.
The transcription is really very nice, the harmony and the melody of the original tune is preserved and even enhanced. Few piano scores for Chinese music can achieve this effect.
The sheet music (or piano score) is originally from http://www.everyonepiano.com, we simply convert to PDF for the convenience of those who are seeking it:
PDF Sheet Music Score for Cai Yun Zhui Yue: Cai Yun Zhui Yue PDF
I checked that this version is the same as the one performed by Li Yundi:
Singapore Maths Tuition 