Abstract: The breakage parameter evaluation is analyzed for structured loess under loading, unloading and wetting by distinct element method (DEM). First, the breakage parameter is defined based on the discrete medium, and the expressions for breakage parameter in representative models for structured soils are introduced. Then the evaluation of breakage parameter for structured loess under loading, unloading and wetting is measured by the micro measurement technique of discrete element method. The relation between the breakage parameter and the macroscopic parameter such as strain or stress is presented, and the forms of formulas for the breakage parameter in representative models for structured soils are examined. Finally the formulas for calculating the breakage parameter under different stress paths and wetting paths are proposed. The parameters in these formulas are few and the formulas can predict the evaluation of breakage parameter for structured loess under loading and wetting well.