Reversible watermarking technique for relational data is intended to protect the copyright. It overcomes the shortcomings of traditional watermarking techniques. It can not only claim the copyright of data, but also recover the original data from the watermarked copy. However, existing reversible watermarking schemes for relational data cannot control the extent of data recovery. Aiming at this problem, a graded reversible watermarking scheme for relational data is proposed in the study. Data quality grade is defined to depict the impact of watermark embedding on the usability of data. Watermark embedding, grade detection, watermark detection, and grade enhancement algorithms are designed to achieve graded reversibility of watermark. Before distributing the data, the data owner can predefine several data quality grades, then embed the watermark into data partitions. A unique key is used in each data partition to control the position and value of the watermark information. If data users are not satisfied with the usability of data, they can require or purchase relevant keys from the owner to upgrade the data quality grade. The watermark in relational data with any data quality grade is sufficient to prove the copyright. Flexible watermark reversion is achieved via partitioned auxiliary data design. A more practical mechanism is devised to efficiently handle the hash table collision, which reduces both computational and storage overhead. Experiments on algorithms and watermark show that the proposed scheme is feasible and robust.