With the increasingly severe situation of Internet security, how to effectively guarantee the information security in the network has become an important topic of current network security research. Traditional cryptographic technologies such as DES (Data Encryption Standard) and RSA (Rivest-Shamir-Adleman) have provided reliable data protection to some extent, but with the development of technology, their security has been increasingly threatened. This article designed a one-time pad encryption system based on DES algorithm and Java programming implementation. The system aims to provide a secure and reliable encryption scheme to protect the confidentiality of data. Firstly, this article introduced the basic principle and encryption process of DES algorithm, and elaborated on the design ideas and implementation steps of the system, including key management, implementation of encryption algorithm, and data encryption and decryption process. Secondly, during the system implementation process, Java programming language was adopted, and key extension and permutation techniques in DES algorithm were utilized to ensure the security of encryption. Finally, the effectiveness and reliability of the encryption system in protecting data privacy were demonstrated through testing and verification of its functionality and security. The design and implementation of this system provided a feasible solution for one-time pad encryption on the Java platform, and had certain practical and promotional value. The experimental results showed that the average response time of the DES algorithm was 15 ms, indicating high efficiency.