In today’s rapidly developing large UAVs field, flight safety and reliability are essential considerations. Flight load is one of the important factors affecting the load capacity of large UAVs, so the research on load prediction technology can improve flight safety and the reliability of air transportation. This paper first introduces the collection and processing method of flight load data, then uses the machine learning method-BP neural network to predict flight load, establishes the BP neural network model to predict flight load with flight parameters, and optimizes the model according to error analysis. Finally, the accuracy and practicability of the model are verified by analysing the fitting of the training set and the test set, and the error distribution of the true value of shear, bending moment, torque and the absolute percentage of the predicted value, and the model is evaluated.