A new herringbone water-sediment separation structure was designed to continuously separate coarse particle from debris flow.Calculation method of structural strength and stability should be determined before it used in debris flow mitigation.Theoretical analysis showed that the calculation methods of draining dyke is similar to that of traditional close-type dam,and debris flow force,which include debris flow gravity,impact force of rock blocks,debris flow dynamical pressure,mainly loaded on the ribbed beam of the herringbone water-sediment separation grid.By simplifying structural mechanical model,calculation formulas of the ribbed beam's strength and stability were determined,which can be used to determine optimal sectional type and dimension of the grid.