Abstract: Alkaline materials, such as cement, are largely used to reinforce geotechnical engineering. The economic life of laterite structure is clearly shortened with alkaline reinforcing materials, and the ruinous causes are desiderated. Based on chemical analysis and principle of accelerated life test, laterite is dipped in supersaturating lye at constant temperature and multiconcentrations for simulating time of laterite erode by alkaline reinforcing materials. Changes in concentrations of effectiveion are tested in leachate, and pores-characteristics and grainsizegradations of laterite are analyzed. Mechanism is put forward to explain how laterite structure is chronically demolished. Underprops of laterite structure, such as Al, Ti, and SiO3, are lost with speedup by alkaline substance. Coating layers of granule, bonded granules, and fillings between grains are clearly destroyed. Laterite is eroded into poorly-graded soil. Exterior polarity of sesquioxides is inchmeal changed by alkaline materials in contact zone, leading to viscous substances degenerating, thus laterite is decomposed and its structure is chronically ruined. Inner hollows and thin piping are largely engendered since reaction products are extruded off structure by seepage. As a result, engineering indices of laterite become bad and seepage failure and engineering collapse may befall.