The invention relates to a biological brick for ecological slope protection of rock slope surface and a preparation method and a construction method thereof. The biological brick for ecological slope protection is a hexagonal brick pressed by specially-prepared base materials, and the surface of the brick is provided with a notch groove and a pit. The biological brick for ecological slope protection consists of two layers, wherein, one layer is a nutrition medium layer, and the other layer is a seed planting layer; the biological brick for ecological slope protection has the characteristics of light mass, air permeability, water and fertilizer reservation, rainwater erosion and soak resistance, rich nutrition and so on, a seed can directly sprout from the surface layer of the biological brick, and a brick body is also ideally suitable for the growth of a plant. The base materials of the nutrition medium layer of the biological brick consists of biological sludge drying organic compost, fine loam, turfy soil, compound fertilizer, water retention agent, cement and pH modifier. The construction method for the biological brick on a rock slope comprises slope trimming, biological hexagonal brick pavement, anchor bolt driving, net suspension, covering and maintenance. The biological brick is provided with the plant seed planting layer, can be quickly molded at one-time construction to restore the vegetation; compared with other rock slope greening methods, the construction method has the characteristics that: the construction method has simple construction and does not need large-scale mechanical equipment, and the construction cost is two thirds of that of the prior guniting slope protection, etc.