The invention provides aqueous diamond polishing liquid, process for preparation and purpose. The main components are diadust, dispersion stabilizer, suspending agent, pH modifying agent, antiseptic agent, organic solvent and deionized water. The preparing technique of the invention is that organic solvent, diadust, prior prepared suspending agent, deionized water and dispersion stabilizer are mixed, then the mixture is stirred or supersonically dispersed uniformly, finally pH modifying agent and antiseptic agent are added, and the preparation is accomplished after shaking up. The lapping liquid can be widely used in grinding and polishing in various departments and areas of optical instruments, glasses, ceramics, rigid alloy, diamonds, artificial lens, optical fiber, LED display, integrated circuit, semiconductor, hard disk and the like. The lapping liquid can be kept in uniform and stable state, generates no precipitation, delamination or invalidation.