Ventilating vacuum method can overcome the clogging problem which often occurs on the traditional vacuum method dewatering dredged clays with high initial water contents. However, how to analyze the anti-clogging behavior of ventilating vacuum method is an important issue in practical engineering. A radial drainage model was established based on the filtration theory developed by Ruth. The vanity of the model was verified using the test results of ventilating vacuum, and the change law in average radical dewatering resistance of dewatering layer which reflects the filtration performance was investigated during the dewatering process. It is indicated that the dewatered layer is compacted by traditional vacuum method during the dewatering process. Its corresponding pore structure is unstable, thus the drainage pipeline often clogs. While the technique of ventilating vacuum provides a powerful way to overcome the clogging problem, and the pore structure is stable during the dewatering process.