Filtration is essential to the efficient operation of drip irrigation systems and screen filter is the most common types of filter used in drip irrigation systems. The screen of filter could be clogged by sand particles which cannot pass through the filter mesh pore in the process of filtering. The clogging experiment was carried out to analyze the process and reason of screen clogging, and obtain some parameters of calculating the pressure drop of screen filter after being clogged. According to experimental results, the clogging reason was analyzed by the medium clogging and filtration cake clogging, respectively. The sizes of sand particles in inner layer of filtration cake were large and the sizes in the outer layer were small and uniform. With the large size of mesh pore, the time of screen clogging was short and the screen was easy to be clogged. Under the same size of mesh pore, the time of screen clogging would be shortened with large sand concentration. Based on Darcy’s law and actual parameters of screen, the relationship between pressure drop of screen and the mesh pore, mesh thickness, mesh porosity, filtration cake thickness, filtration cake porosity was developed theoretically. According to the actual data of the filtration mesh and cake, the pressure drops between the internal and external surfaces of screen were calculated with the mesh pore sizes of 430μm, 280μm and 200μm, respectively. The results indicated that the pressure drops were increased with the increase of flow rate, mesh thickness and filtration cake thickness. The pressure drops also were increased with the decrease of mesh pore and cake porosity. The calculated results of pressure drop were compared with the measured values, which indicated that the predicted pressure drop for each filtration level showed a good correlation with the measured pressure drop of filter screen, and the results can reflect the clogging law of screen.