The automation of some traditional artificial observations such as clouds and weather phenomena has profound influence on the daily observation operation, which affects data storage and data exchange as well. The characteristics of the World Meteorological Organization code table 4680 are discussed, and it is discovered that it is more suitable for automatic weather observation. Based on the newly formed rules and regulations in atmospheric observation, the automatic coding of present weather and past weather is designed. Taking the coding principles and weather characteristics into accounts, the antomatic coding of 46 codes is realized automatically.