The invention relates to a permeable alkali slag concrete suitable for heavy load pavements. The concrete is composed of the following components by mass: 70-79 parts of aggregate; 16-20 parts of slag; 0-4 parts of an admixture; 0-0.08 part of an additive; 3-6 parts of an activator; and 3-4 parts of water. The invention also discloses a preparation method of the permeable alkali slag concrete. The method uses alkali slag as the cementitious material, and optimizes the water glass, slag and gravel components to prepare the permeable concrete. Compared with problems of low compressive strength, poor durability and difficult applicability to heavy load pavements in existing permeable concrete, the permeable alkali slag concrete obtained by the invention has certain water permeability, high compressive strength and good wear resistance. The permeable concrete also has good anti-stripping ability and excellent long-term usability.