The invention belongs to the environment protection and ecological construction field, and provides a method for preparing an ecological brick for ecological ditch construction, an ecological protective slop, etc. The ecological brick consists of two part: one part is a brick body with a planting groove; the other part is a filler for the planting groove; a material of the brick body can be concrete or a mixed material brick consisting of fly ash, lime, phosphogypsum and sand; and the strength of the material can reach between 10 and 20 MPa. The shape of the brick body can be a hexahedron, a cuboid, a cube, a trapezoid, etc; the planting groove of the brick body can be positioned on one side, two sides or more sides of the brick body; the shape of the planting groove can be a column, a cone, a hexagonal prism, etc; the bottom of the groove is fixed with a ferrite permanent magnet; and the magnetic density of the surface of the ferrite permanent magnet is between 0.03 and 0.08 T. The filler of the planting groove consists of a mixed substrate which can hold water, penetrate and supply plant nutrition, have certain strength and is favorable for plant growth and plant seeds. The bricks are bricked to an intercepting drain, a drainage ditch, a diversion ditch, etc. through proper combination; during a week after proper maintenance, plant can germinate; after about six months, the ecological ditch and other ecological structures covered with plants and coordinated with the periphery are formed.