A impact-based method, which can be used to measure the real-time velocity and the mass flow rate of the granules flow, was presented. And a way to dynamically estimate the measurement error of the velocity and mass flow rate was also provided. Using the self-designed experimental equipment, experiments with the soy bean as the experimental object to estimate the measurement error had been done. It was shown during the experiments that the maximal estimated error of the mass flow rate was 4.00% and the average value was 1.44%, the maximal estimated error of the velocity was 9.69% and had an average value of 5.03%. A positive correlation between the dynamic measurement accuracy and the measurement accuracy of gross mass was also found.