流水行云

流水行雲
liúshuǐxíngyún
  1. (of calligraphy, writing, etc.) very smooth and natural; natural and unforced style
  2. very smooth and natural; natural and unforced style

Wiktionary

Entry Composition

1 流水 liúshuǐ
  1. running water
  2. (business) turnover
2 行云 xíngyún
  1. (literary) a drifting cloud
  2. a drifting cloud