TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: After the processing step using aqueous alkali solution and before the mixing step, the method further comprises processing acid treatment to montmorillonite solution to obtain a pH of 8.5-9. The aqueous alkali solution processing uses sodium hydroxide aqueous solution and/or ammonium hydroxide aqueous solution. The concentration of aqueous alkali solution is 0.05-1.5 M; and alkaline treatment time is 1-24 hours. The acid solution used in acid treatment is ammonium nitrate (NH4NO3), acetic acid, or oxalic acid aqueous solution. The step for preparing crystallization stock solution further comprises adding silicon source, which is silica sol, activated silicon dioxide, and/or metasilicic acid ethyl ester. The silicon source in montmorillonite in the step of aqueous alkali solution processing occupies 20-100% of the total silicon source. The mol ratio of template agent based on triethyl amine, silicon source based on silicon dioxide, aluminum source based on alumina (Al2O3), phosphorus source based on phosphorus pentoxide (P2O5), and water in the prepared crystallization stock solution is 2.5-4.5:0.3-0.6:0.8-1.2:0.9-1.1:30-200. The aging step is conducted for 0.5-24 hours at room temperature to 80 degrees C. Crystallization heating is conducted for 24-96 hours at 180-220 degrees C. After crystallization heating step and before molding step, the method further comprises a step of reducing the temperature of the mixture. The template agent is selected from triethylamine, diethylamine, tetraethyl ammonium hydroxide, and/or morpholine. The aluminum source is selected from diaspore, aluminum isopropoxide, and/or hydrated alumina. The phosphorus source is selected from phosphoric acid, phosphate, and/or phosphorous acid. The binding agent for molding is selected from silica sol, aluminum sol, silicon, and/or aluminum sol. It is added at 10-30% of montmorillonite. The molding step comprises spray drying. The spray drying step comprises air stream mode, centrifuging mode, or pressure mode. After the molding step, the method further comprises processing catalyst (C1) by 0.05-0.5 M acid aqueous solution so that its active component becomes HSAPO-34 molecular sieve, where acid aqueous solution is NH4NO3, acetic acid, and/or oxalic acid, where mass ratio of (C1) to acid aqueous solution is 0.5-1:1. The acid aqueous solution soaks (C1) for 1-24 hours at room temperature; and dries for 10-24 hours after filtering at 100-150 degrees C. After the molding step, the method further comprises processing (C1) by nitrate or sulfuric acid aqueous solution of groups IB, IIB, IIIB, IVB, IIA, and VIIIA to make the active component of (C1) be metal improved SAPO-34 molecular sieve, where metal salt solution process comprises soaking (C1) for 1-24 hours at room temperature, and drying for 10-24 hours at 100-150 degrees C. The method further comprises burning (C1) having HSAPO-34 or metal improved SAPO-34 as active component at 500-600 degrees C for 4-6 hours, to improve and activate the hole structure of the molecular sieve. Preferred Composition: The catalyst (C1) has grain diameter of 10-150 mu m.