The invention discloses a preparation technology of high-purity flomoxef sodium. The preparation technology includes following steps: on the basis of a flomoxef intermediate, performing an acidifying reaction to obtain a reaction liquid; performing a water washing process, an extraction process, an aseptic filtration process and the like to the reaction liquid; and performing a solventing-out crystallization step through a one-step crystallization process to obtain a flomoxef sodium product with a purity being higher than 99.90%, wherein key points in the solventing-out crystallization step are selection and proportion of a solventing agent and dropwise addition of a salifying agent and the solventing agent at the same time with crystal growing. The preparation technology overcomes problems which are difficult to control during the solventing-out crystallization step of the flomoxef sodium. The flomoxef sodium is prepared in one step with the flomoxef intermediate as a raw material and the purity of the product of the flomoxef sodium reaches higher than 99.90% just through one crystallization step, which is cannot be achieved through a freeze-drying method or a common solventing-out crystallization process in the prior art. Quality of the product is in conformity with or even exceeds a standard in japanese pharmacopoeia JP16. The preparation technology has a more wide application prospect.