A separation reagent for separating cobalt from iron, zinc, calcium, silicon and magnesium, comprising an extracting agent and a co-extracting agent; wherein the extracting agent comprises BC196, and the co-extracting agent comprises Mextral 6103H. The separation reagent of claim 1, wherein a volume percentage of the BC196 in the separation reagent is 5-15%, and/or, a volume percentage of the Mextral 6103H in the separation reagent is 5-8%. The separation reagent of claim 2, wherein the separation reagent further comprises a diluent; and a volume percentage of the diluent in the separation reagent is a balance after subtracting the volume percentages of the extracting agent and the co-extracting agent; and the diluent comprises at least one of kerosene, sulfonated kerosene, Escaid 110, heptane, hexane, dodecane, or sec-octanol. Use of the separation reagent of any one of claims 1 to 3 in separating cobalt from iron, zinc, calcium, silicon and magnesium. A method for resource utilization of a magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon, comprising a following step: extracting the magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon with the separation reagent of any one of claims 1 to 3, to obtain a loaded organic phase and a raffinate water phase; wherein a volume ratio of the separation reagent to the magnesium sulfate solution containing cobalt, iron, zinc, calcium, and silicon is 1:0.5 to1:20; the extracting comprises a single-stage extraction or a multi-stage counter-current extraction; and a pH value of the raffinate water phase is 4.5-5. The method for resource utilization of the magnesium sulfate solution of claim 5, further comprising subjecting the separation reagent to a saponification treatment prior to the step of extracting; wherein a saponifying agent used for the saponification treatment is an alkaline solution; the alkaline solution comprises at least one of a sodium hydroxide solution, ammonia water, a potassium hydroxide solution, or a magnesium hydroxide solution; the alkaline solution has a concentration of 5-10 mol/L; and a degree of saponification after the saponification treatment is greater than 0 but not greater than 50%. The method for resource utilization of the magnesium sulfate solution of claim 5 or 6, further comprising carrying out a reverse extraction on the loaded organic phase with a reverse extracting agent to obtain a battery-grade cobalt sulfate solution; wherein the reverse extracting agent comprises at least one of a sulfuric acid solution, or a hydrochloric acid solution; a concentration of H + in the reverse extracting agent is 3-5 mol/L; a number of stages of the reverse extraction is 1-5. The method for resource utilization of the magnesium sulfate solution of claim 7, further comprising washing the loaded organic phase with a washing liquid prior to the reverse extraction; wherein the washing liquid used for washing comprises at least one of water, a sulfuric acid solution, a hydrochloric acid solution, a phosphoric acid solution, or an oxalic acid solution; a concentration of H + in the washing liquid is not greater than 1 mol/L; a volume ratio of the washing liquid to the loaded organic phase is 0.05:1 to 0.5:1; the washing is multi-stage counter-current washing; a volume ratio of the reverse extracting agent to the loaded organic phase after washing is 0.05:1to 0.5:1. The method for resource utilization of the magnesium sulfate solution of claim 5 or 6, further comprising performing ion adsorption on the raffinate water phase to obtain a refined magnesium sulfate solution. The method for resource utilization of the magnesium sulfate solution of claim 9, wherein an ion exchange resin used for the ion adsorption is a sodium- type resin; and the sodium-type resin comprises at least one of D467, SepliteD001, LSC850, or D503.