Abstract: The most effective cascade scheme for the enrichment of recycled uranium is the cascade with an additional flow, in which the natural uranium is supplied as a base feed flow and the recycled as an additional feed flow. Based on particularities in the enrichment of recycled uranium, an approximate calculation method of M cascade for the enrichment of recycled uranium was presented. Numerical calculations indicate that the results obtained by using the approximate method and the engineering optimization method are very approach, and the maximum relative error is less than 0.1%. But compared with the engineering optimization method, the approximate method is more simple, convenience and faster.