The invention discloses a process for producing potassium sulfate by decomposing potassium feldspar at low temperature with fluorine-containing acid. The process comprises the following steps of: decomposing potassium feldspar powder by utilizing fluorine-containing acid, wherein the ratio of the acid to the potassium feldspar powder is 1-5:1; reacting for 1-6h at 60-100 DEG C, absorbing the generated SiF4 gas with water to obtain H2SiF6 and a white carbon black product; separating a slurry obtained by reaction to obtain liquid, a slurry substance and a solid substance; returning the liquid and the solid substance to a reaction kettle for secondary decomposition and separation; and decomposing the potassium feldspar to finally obtain the acidic liquid, a slurry substance and a solid substance; purifying and separating the solid substance through the fluorine-containing acid to prepare a potassium fluosilicate product; recycling the obtained acid liquor to the decomposition reaction ofthe potassium feldspar; carrying out full alkaline hydrolysis reaction on the K2SiF6 and KOH under the heating condition and then separating to obtain a KF solution and SiO2.nH2O; reacting the KF solution and Ca(OH)2 and then separating to obtain a KOH solution and a CaF2 solid; dripping concentrated sulfuric acid to a potassium hydroxide solution to neutrality; concentrating through evaporation,crystallizing, centrifuging and drying to obtain a potassium sulfate product. The three wastes are not generated in the production process, and the invention solves the technical problems of high energy consumption, low yield and recovery rate, and the like in the prior art.