Objective To study the real-time predictive compensation methods for calculating the errors caused by system delay and materials stayed in the air during the operation of packaging machine. Methods Through analyzing the fall height of granular materials, the impacts of the system delay and materials stayed in the air on the packing precision and their and changes were studied, and the determinant factors of packaging error caused by them were identified. Results System delay and materials stayed in the air led to excessive final materials than the value of the real-time detection by the system and the error depended on the system delay, the material fall time and the material accumulating rate, and the error decreased with the increase of granular material in the bag. Conclusion The time Δ t of system delay and the material fall time can be regarded as the function of material weight m, so we can calculate the relation of Δ t and m in advance, and then calculate the corresponding Δ t when predictive compensation is needed. Finally, through Δ t and the material accumulating rateυ m of the previous period of time, we can calculate the error Δ m caused by Δ t, thus achieving the purpose of real-time predictive compensation of the system delay and the material in the air.