Research on very fine fossil corals from Shiqiantan Fm, Xinjiang (310Ma) which have very clear growth lines caused by diurnal increments of calcium carbonate deposition provides important information about ancient climate. This result breaks the record of the oldest remaining material for detailed climate analysis. Data showed distinct seasonal variations, separating ancient climate into four seasons. Storms are frequent in summer during at that time. And the sea temperature exceeded ~30°C for a month in mid-summer. Equipped with this new method, a specific day’s climate, cloudy or shining, can be studied from the diurnal patterns.