The invention discloses a monitoring and fault diagnosis system of a PLC control system of a tower crane, and particularly relates to the field of tower crane PLC control. The monitoring and fault diagnosis system of the PLC control system of the tower crane comprises a PLC, a rotary control system, a variable amplitude control system, a hoisting control system and a human-computer interaction module, wherein a display module, a PLC controller input monitoring module, a PLC controller output monitoring module and a master control input module are arranged in the human-computer interaction module. According to the monitoring and fault diagnosis system of the PLC control system of the tower crane, engineering technicians can quickly master the operation state of the tower crane, and engineering technicians can conveniently and rapidly carry out effective monitoring and fault diagnosis on the tower crane.