NOVELTY - Comprehensive utilization of phosphatic fertilizer by-product i.e. fluosilicic acid includes reacting fluosilicic acid treated by dephosphorization with potassium chloride under crystal seed condition; growing crystal; filtering to obtain solid potassium fluosilicate; drying potassium fluosilicate; dewatering; removing impurity; transferring the dried potassium fluosilicate and inert additive i.e. potassium fluoride back to a rotary furnace; controlling the temperature of the material in the furnace; and decomposing the potassium fluosilicate.    USE - Comprehensive utilization of phosphatic fertilizer by-product i.e. fluosilicic acid (claimed).    ADVANTAGE - The method produces high-quality silicon tetrafluoride, potassium fluoride, hydrogen fluoride, and agricultural potassium sulfate using low-cost raw material. It has high resource utilization rate.    DETAILED DESCRIPTION - Comprehensive utilization of phosphatic fertilizer by-product i.e. fluosilicic acid comprises:    (A) reacting 5-25% fluosilicic acid treated by dephosphorization with potassium chloride under crystal seed condition; growing crystal; and filtering to obtain solid potassium fluosilicate;    (B) drying potassium fluosilicate at 150-250?0 C; dewatering; and removing impurity;    (C) transferring the dried potassium fluosilicate and inert additive i.e. potassium fluoride at 45:55 mass ratio back to a rotary furnace; controlling the temperature of the material in the furnace at 450-750?0 C; and decomposing the potassium fluosilicate to obtain silicon tetrafluoride gas and crude product i.e. potassium fluoride;    (D) purifying, cooling, and compressing the silicon tetrafluoride gas to obtain silicon tetrafluoride product;    (E) dissolving the crude product i.e. potassium fluoride and recrystallizing to obtain industrial potassium fluoride product; or introducing to an acidolysis rotary reaction furnace and performing acidolysis reaction with sulfuric acid at 220-280?0 C to obtain agricultural potassium sulfate product and hydrogen fluoride gas containing silicon tetrafluoride; or dissolving one part of potassium fluoride with water and recrystallizing to obtain industrial potassium fluoride product, introducing the other part to the acidolysis rotary reaction furnace, performing acidolysis reaction with sulfuric acid at 220-280?0C to obtain agricultural potassium sulfate product and hydrogen fluoride gas containing silicon tetrafluoride; and    (F) purifying the hydrogen fluoride gas containing silicon tetrafluoride; and separating to obtain hydrogen fluoride product.