Aiming at the problem of emitter jamming in micro-irrigation engineering, the optimal number of laminated sand filter was discussed with stated filter diameter, through abundant hydraulic characteristics tests and back flushing tests. Equations of hydraulic characteristics in sand filter lamination and formulas of filtrated head-loss are put forward in the study. The results of experiments show that the suggested formulas of filtrated head-loss are more precise than the former empirical formulas: the relative error is 3.18% with specified velocity. This study offers references for research and development of new types of sand filter.