A method and a system for encryption and decryption based on continuous-variable quantum neural network CVQNN. The method includes: updating a weight of the CVQNN with a training sample; triggering, by a sender, a legal measurement bases synchronization between the sender and the CVQNN; converting, by the sender, the information to be sent into a quadratic plaintext according to the synchronized measurement bases, and sending the quadratic plaintext to the CVQNN; encrypting, by the CVQNN, a received quadratic plaintext, and sending an encrypted quadratic plaintext to a receiver; after receiving the encrypted quadratic plaintext, sending by the receiver the encrypted quadratic plaintext to the CVQNN for decryption to obtain decrypted information. The embodiments implement data encryption and decryption by introducing CVQNN model and synchronization measurement technology. The embodiments provide advantages of high reliability, high security and easy realization.