The invention relates to a high temperature-resistant amide humate oil-base mud fluid loss additive and a preparation method thereof, belonging to the technical field of humic acid fluid loss additives and aiming at solving the technical problem of improving the high temperature-resistant characteristic of an amide humate oil-base mud fluid loss additive. According to the technical scheme, the preparation method of the high temperature-resistant amide humate oil-base mud fluid loss additive comprises the following steps of: 1, preparing an amide humate solution, slowly adding a urea solution to a sodium humate solution at certain temperature, sufficiently dissolving and then cooling to room temperature, and pouring out the upper amide humate solution; 2, preparing a fluid loss additive, and slowly adding a ferrous solution to the amide humate solution under the condition of stirring for reacting to obtain a complexing solution; drying the complexing solution to obtain the high temperature-resistant amide humate oil-base mud fluid loss additive. The high temperature-resistant amide humate oil-base mud fluid loss additive disclosed by the invention can be used for increasing the tolerable temperature of amide humate, and thus the amide humate can be used under the condition of higher temperature.