The invention relates to a water-based epoxy emulsion type carbon fiber sizing agent and a preparation method thereof. The water-based epoxy emulsion type carbon fiber sizing agent comprises the following components in percentage by weight: 15%-35% of epoxide resin, 5%-20% of surface active agent, 0.1%-0.5% of lubricating agent, 0.1%-0.5% defoaming agent and 55%-65% of deionized water. According to the water-based epoxy emulsion type carbon fiber sizing agent and the preparation method thereof, no volatile organic compound is added, so that the harm to production equipment and operators in preparation and application processes of the sizing agent is greatly reduced, and the environment protection is facilitated. The water-based epoxy emulsion type carbon fiber sizing agent and the preparation method thereof which are disclosed by the invention have the advantages of simple emulsifying process, safety in operation, low requirement on the production equipment, easiness for raw material obtaining, low price and suitability for large-scale production.