The impermeability experiments were conducted by adopting a HS-4 concrete permeability instrument and the permeability labeling method on the concrete block covered with composite mortar mixed without additives and with new additive respectively, with emphasis on the thickness of the added mortar and incorporation of additives. The obtained permeability grades of all specimens were then investigated. The results showed that the concrete impermeability was improved effectively by applying high performance composite mortar with 20 mm thickness and 18 % additive content on the concrete surface. Furthermore， the reinforced mesh thin layer of high performance composite mortar reinforced the concrete structure effectively.