The invention discloses an ecological building block, which comprises a building block unit, wherein a plant growth cavity is arranged in the middle of the building block unit; the front wall of the plant growth cavity is of the appearance surface, the rear wall thereof is of the earth retaining surface, the two side walls thereof are provided with ecological holes, and a communication hole is communicated with the plant growth cavity on the earth retaining surface. After the ecological building block is adopted for building a retaining wall or a channel revetment, the root system of a plant in the plant growth cavity can be connected with a retained earth body by the communication hole and stretches into the retained earth body, so that the plant can more fully absorb the water and the nutrition in the back earth, can grow better and can quickly cover the wall surface and shielding the building block, so as to form the gardening retaining wall quickly in a sustainable way with low cost, thereby providing a better ecological environment for aquatic. Meanwhile, the root system of the plant is more developed and can stretch into the retained earth body; and the longer the time is, the firmer the revetment or the wall body is connected with the back earth.