The invention provides an oat-based fat substitute and a preparation method thereof, wherein the fat substitute is prepared by the following steps: (1) cleaning and cooking; (2) preliminary enzymatichydrolysis and pulp grinding; (3) additional enzymatic hydrolysis; (4) Maillard reaction; and (5) finished product preparation, thereby obtaining the oat-based fat substitute. The invention has the following advantages: the fat substitute does not contain any lipids, and is more green and healthy; the fat can be completely and singly substituted, and the mouthfeel is closer to the fat; and the preparation method adopts the enzymatic hydrolysis twice, the material-liquid ratio is high, the pulp grinding time is saved by 20% or above, and the finished product is easier to concentrate and low inenergy consumption.