The invention discloses a preparation technique of fosphenytoin sodium. The technique comprises the following steps: carrying out hydroxymethylation on the initial raw material phenytoin to obtain 3-hydroxymethyl-phenytoin, reacting with phosphorus oxychloride and 1,2,4-triazole, and finally, salifying to obtain the fosphenytoin sodium. The technique has the advantages of simple operation steps, cheap and accessible raw materials, high yield, high product quality, low production cost, high safety, environment friendliness and the like, and is especially suitable for industrial production.