With the development of the internet, many important documents can be exchanged online. It is vital to protect the safety and genuineness of the seals in the published documents. In this paper, a new electronic seal system based on the RSA digital signature algorithm and public-key infrastructure is presented. The RSA digital signature algorithm and its mathematic foundation are discussed in detail and the feasibility of the electronic seal scheme implementation based on public-key infrastructure is given. The scheme combines one-way hash function and digital watermarking, implements the tamper-proofing of electronic documents, anti-copy of electronic seal and secure access control function, can effectively to meet the basic needs of electronic document and security requirements.