The invention relates to a fabric dirt pretreatment agent containing a steady biological enzyme complex and a low-activity substance and a preparation method thereof. A product of the invention takes fatty alcohol polyoxyethylene ether (7), fatty alcohol polyoxyethylene ether (9), sodium fatty alcohol-polyoxyethyleneether sulfate (70 percent), fatty alcohol polyoxyethylene ether (JFC), polyacrylate, sodium citrate, boric acid, propylene glycol, prolease, calcium chloride, isothiazolinone, essence, and deionized water as raw materials; and the method adopts a polymer to ensure that the prolease forms a polymer complex in a system by researching biological enzyme stabilization technology, which ensures the long-term effective activity of biological enzyme, ensures that the product can achieve stronger detergency when the content of an active substance is 10 percent or so and has steady quality during the storage, and achieves the aims of saving resources and protecting environment. The product is neutral, and has unique advantages in preventing fading, reducing the damage of clothes, protecting skin, and reducing pollution.