The invention provides a composite alkaline cleaning agent for glass bottles and a preparation method thereof, and is characterized in that the composite alkaline cleaning agent is prepared by reaction of water, potassium hydroxide, a surfactant, an oxidant, a complexing agent, a penetrating agent and the like in accordance with a certain proportion and a certain process and requirements. The composite alkaline cleaning agent is mainly used for assistant industrialized cleaning of recovered glass bottles of beer, beverages and condiments; the composite alkaline cleaning agent is specially researched and developed for bottle washing and mark shedding, as well as for watermarking bottles which are difficult to clean due to mould spot, oil stain and tap water evaporation, strongly cleans thewatermarking bottles caused by mould spot, oil stain and tap water evaporation, has the advantages of low use cost, high cleaning rate, good safety, good alkali stability, good thermal stability and strong permeability.