The invention belongs to the field of new energy automobiles, and particularly relates to a method for road load spectrum of a battery pack support structure of a pure electric truck. The method is based on a multi-body dynamics principle. A rigid-flexible coupling multi-body dynamic model consisting of a seven-channel virtual test bed, a battery pack bracket and a whole frame is established. Themethod comprises the following steps: by taking battery pack bracket acceleration collected by a test field as a target response signal, reversely obtaining force boundaries of a virtual test bed andactuators of a frame by adopting a virtual iteration method, namely, a road load spectrum for fatigue analysis of a battery pack bracket; and based on the obtained load spectrum, analyzing the fatiguelife of the battery pack support structure. According to the method, the correlation between the fatigue analysis of the battery pack bracket structure of the pure electric truck and the road durability test of a real vehicle test site is ensured. The problem that the fatigue life of the battery pack bracket structure cannot be quantified by a traditional method is solved. The development periodis effectively shortened and development cost is reduced.