The invention relates to a thickener used for all-cotton and artificial cotton printing, and a preparation method thereof, and belongs to the technical field of reactive dyes. The thickener for printing comprises inorganic gel bentonite, carboxymethylcellulose sodium, an acrylic polymer and peregal O-25. The thickener has the advantages of convenience in preparation, high color yield, bright color, complete patterns, good level dyeing property, good thickener removal property, electrolyte resistance, high cost performance, environmental protection and low economy cost.