Humic acid is the remains of plants and animals, mainly the remains of plants, through the decomposition and transformation of microorganisms, as well as a series of organic substances that are caused and accumulated by the process of geochemistry. Its total volume is staggering, trillions of tons. Rivers and lakes, soil coal mines, most of the surface has its traces. Because of its widespread existence, it has a great influence on the earth, involving carbon cycle, mineral migration accumulation, soil fertility, ecological balance and so on. The soil contains the largest amount of humic acid, but the content is less than one percent, and the total amount in brackish water is not small, but the concentration is lower. The humic acid resources most likely to be exploited are low-calorific coal, such as peat, lignite and weathered coal. Among them, humic acid content reaches 10-80%. China's coal reserves are very rich. According to the data, there are 5 billion tons of peat, 126.5 billion tons of lignite, and no statistical data on weathering coal. In this sense, the production and application of humic acid can also be said to be one aspect of coal chemical industry.
The basic structure of humic acid macromolecules is aromatic ring and fat ring, which is composed of carboxyl, hydroxyl, carbonyl, quinone, methoxyl, etc.