An encrypted data storage system and method based on offsite key storage are provided, comprising the system includes a key control center, an offsite key storage system, and a data encryption/decryption storage system. The offsite key storage system includes a first key control device, a key storage device, and a first quantum key distribution device. The data encryption/decryption storage system includes a second key control device, a data encryption/decryption storage device, and a second quantum key distribution device. The first quantum key distribution device is in quantum communication connection with the second quantum key distribution device. The first key control device is communicatively connected with the key storage device and the first quantum key distribution device, respectively.