A Paillier decryption system, IC, and method. The IC includes: a modular exponentiation module, for performing modular exponentiation operations related to a first subitem and a second subitem, where a Paillier decryption process of encrypted data is divided into a first subitem and a second subitem according to the Chinese remainder theorem, the first subitem corresponding to a first prime, the second subitem corresponding to a second prime, a public key of the encrypted data being a product of the first prime and the second prime, a bit width of the first prime being the same as a bit width of the second prime; a first module combination corresponding to the first subitem, for determining a computation result of the first subitem; and a second module combination corresponding to the second subitem, for determining a computation result of the second subitem.