The invention discloses a method for preparing potassium sulfate from brine with a low sulfur-potassium ratio. The method includes steps of (1), evaporating the raw brine to obtain potassium-mixed salt mine; (2), sun-curing carnallite; (3), feeding the carnallite to a potassium chloride workshop, and carrying out crushing, decomposing, flotation and dehalogenation on the carnallite to obtain potassium chloride concentrate; (4), feeding the potassium-mixed salt mine to a picromerite workshop, crushing the potassium-mixed salt mine, mixing the potassium-mixed salt mine and tailings with one another in water after the tailings obtained at the step (3) are subjected to dehalogenation, and carrying out grinding, transformation, flotation, separation and washing to obtain picromerite concentrate; (5), mixing the picromerite concentrate and the potassium chloride concentrate with each other in water to obtain mixtures and transforming the mixtures to obtain potassium sulfate products. The method has the advantages that technical routes of existing processes for producing potassium sulfate from salt lakes are improved, accordingly, shortcomings of methods for producing the potassium sulfur from brine with a low sulfur-potassium ratio in the prior art can be overcome, and the reasonable and feasible method which includes simple processes and short procedures and is low in cost and free of pollution can be provided for producing the potassium sulfate from the brine with the low sulfur-potassium ratio from salt lakes.