The invention discloses an encryption and decryption method based on a unified chaotic system. Chaos modulation and chaos covering technologies are adopted to achieve multi-level encryption; the characteristics of a unified chaotic system are utilized, the unified chaotic system is switched among different types of chaotic systems by modulating system parameters, the system property is more complex, meanwhile, synchronization with a sending end system is realized by utilizing an encrypted signal, and a decryption signal is obtained by utilizing the synchronized system and adopting a decryptionprocess opposite to that of the sending end. The method can be used for secret communication in the national defense communication field and can also be applied to the civil secret communication service industry, secret signals can be disguised as random white noise in reality due to the pseudo-random property of the chaotic system, and the method has good application value.