Provided is an arid area plant root water retention planting pit. The east, the south, the west and the north of the pit edge of the planting pit are respectively provided with a fixing soil groove, the bottom and the inner wall of the planting pit are provided with a whole square geosynthetic clay liner, the four corners of the square geosynthetic clay liner are arranged in the fixing soil grooves respectively, the surfaces of the four corners of the square geosynthetic clay liner are respectively provided with a corner pressing cover soil layer, and the tops of the corner pressing cover soil layer are flush with the pit edge of the planting pit. When the planting pit is adopted in an arid area, moisture can be effectively prevented from leaking, a long-acting water retention function is achieved, growth of plant roots is not influenced, the structure is easy and convenient to achieve, cost is low, the planting pit is environmentally friendly and free of pollution, and the survival rate of plants in the arid area is improved.