An alternative ultrafiltration membrane integrity test utilizing magnetic nanoparticle as a surrogate has been investigated in previous studies, but the absence of a feasible estimation model for the degree of membrane damage causes that this simple membrane integrity test would be not applied easily. This study proposed a calculating model to predict membrane defect size, and investigated the theoretic resolution of the integrity test method. The results obtained with the evolved prediction model D, which is based on Darcy’s law and Bernoulli equation, were satisfactory in predicting the membrane defect size. In this study, this integrity test method had about 39.33% probability to have a theoretic resolution of 3 μm or less under common experimental conditions.