Monitoring a 3D printer comprises a network information module, a photographic device, a status report module, and a fixed format instruction receiver module. The photographic device is capable of periodically shooting a print status of the 3D printer. The status report module is capable of periodically reporting the print status or instantly reporting a print error of the 3D printer. The fixed format instruction receiver module is capable of receiving a remote fixed format instruction to operate the 3D printer. Thus, the system may not require an operator to monitor the 3D printer for long. Even on the remote end, the system can monitor a print status of a printed object and may execute a corresponding treatment when a print error of the 3D printer has occurred.