The invention discloses a system and a method for automatically testing main control hardware of a fan on the basis of a PLC (Programmable Logic Controller). The testing system comprises a PLC main controller, an extendable data interaction module and a graphical debugging terminal; the data interaction module and a data interaction module of equipment to be tested are subjected to one-to-one interaction by a cable; and the PLC main controller of the testing system is used for rapidly acquiring information of the data interaction module of the testing system in an EtherCAT manner, respectively communicating with a main controller of the equipment to be tested and the graphical debugging terminal on the basis of an ADS (Automation Device Specification) protocol and implementing automatic testing on a loop of the main control system hardware of the fan. The system and the method have the advantages of good extendibility, strong applicability, high repeated utilization rate, reduction on debugging time, improvement on working safety and quality of a main control system of the fan and the like.