This present application relates to the field of data encryption and decryption technology, and in particular, relates to a selective data encryption and decryption method and apparatus. The encryption method includes: generating a string of true random numbers 0, 1 of a predetermined length via the preset method as a random seed; acquiring data for several times from the random seed, and cascading the data acquired each time into a random string no shorter than the length of a plaintext; according to the random string, generating a plaintext encryption bit identifier random string; randomly selecting more than one half of plaintext data for encryption according to the plaintext encryption bit identifier random string; arranging the encrypted data and unencrypted data to form a ciphertext according to their positions of the plaintext. The encryption apparatus includes: true random number generation module, encryption bit identifier random string generation module, plaintext selectivity encryption module and ciphertext formation module. This application also provides a selective data decryption method and apparatus. This invention reduces the amount of data to be encrypted or decrypted, thus improves the data encryption and decryption performance.