The invention belongs to the field of chemical fiber pulp dreg production in the textile industry, and in particular relates to a cooking method for preparing cotton linter pulp dreg by using a composite auxiliary agent. The cooking method comprises the following steps: preparing the composite auxiliary agent, preparing a composite auxiliary agent liquid, preparing a mixed liquid of lye and the composite auxiliary agent liquid, performing material feeding, and making paper with pulp to obtain the finished product. The method can effectively achieve the aims of reducing cost, improving quality, saving resources, reducing pollutant discharge and improving benefit while reducing the consumption of cotton linter and alkali and reducing a cooking black liquor COD and the chrominance; besides, the method is suitable for popularization and application.