The invention discloses soybean yoghourt and a preparation method thereof. The soybean yoghourt is prepared through fermenting raw materials in a formula with a fermenting agent. Each 1000 parts by weight of the formula of the soybean yoghourt comprises the following raw materials in parts by weight: 90-180 parts of soybeans, 70-90 parts of white granulated sugar, 9-24 parts of a stabilizing agentsystem, 10-16 parts of composite soybean corn oil, 1-3 parts of table salt and the balance of water. The soybean yoghourt is free from flavored substances of milk and the like, pure soybeans are directly used as the raw materials, and through compounding combination of the raw materials, selection of the stabilizing agent, and adjustment and control of preparation technology parameters, the soybean yoghourt product free from beany flavor can be directly prepared. The invention further provides a preparation method of the soybean yoghourt. The preparation method comprises the technology characteristics that a special technology is used for processing soybean milk free from beany flavor, and further the soybean milk free from the beany flavor and the self-made stabilizing system are used for making the soybean yoghourt. According to the method, the denaturing of soybean protein is reduced, the utilization rate of the soybeans is increased, the best mouth feel is guaranteed, and besides,the soybean yoghourt products being high in cost-effectiveness can be obtained.