An automatic circuit board test method carried out by an automatic circuit board test system, the automatic circuit board test system including at least one switch module of board under test which includes at least one relay module including a plurality of relays (111a/111b), and a software protector connected with the at least one relay module, a control module, a test process module connected with the control module, a first serial port bus, a second serial port bus, and a third serial port bus, the at least one switch module of board under test being connected with a test board which includes a repeater, a first signal interface connected with the repeater, a second signal interface and a third signal interface mutually connected, the at least one switch module of board under test being connected with the second signal interface and the third signal interface, respectively, the first serial port bus being connected between the software protector and the test process module, the second serial port bus being connected between the test process module and the control module, the third serial port bus being connected between the test process module and the first signal interface, the software protector being a dongle, the control module being connected to the at least one relay module, the automatic circuit board test method comprising steps of: setting a test mode by connecting the test process module with the first signal interface through the third serial port bus to make the repeater set to enter the test mode; transmitting a control signal to a micro-controller of the control module by the test process module; converting the control signal into a serial control signal by the micro-controller of the control module; comparing data by connecting the micro-controller of the control module with a storage device of the control module, and then transmitting the serial control signal to the at least one relay module by the micro-controller; switching a signal path by the at least one relay module controlling an output connection pin of an expansion chip of the at least one relay module according to the serial control signal to make switches of the plurality of the relays (111a/111b) which include a first relay and a second relay, and then transmitting the serial control signal to the test board by the at least one relay module; executing a testing action in the test board; receiving a result data which is tested by the test board by the at least one relay module, and then transmitting the result data which is carried in a serial return signal to the software protector by the at least one relay module; packaging the result data by the software protector to form an encryption result data, and then converting the serial return signal into a return signal, and then transmitting the encryption result data to the test process module through the return signal; and storing the encryption result data by the test process module. setting a test mode by connecting the test process module with the first signal interface through the third serial port bus to make the repeater set to enter the test mode; transmitting a control signal to a micro-controller of the control module by the test process module; converting the control signal into a serial control signal by the micro-controller of the control module; comparing data by connecting the micro-controller of the control module with a storage device of the control module, and then transmitting the serial control signal to the at least one relay module by the micro-controller; switching a signal path by the at least one relay module controlling an output connection pin of an expansion chip of the at least one relay module according to the serial control signal to make switches of the plurality of the relays (111a/111b) which include a first relay and a second relay, and then transmitting the serial control signal to the test board by the at least one relay module; executing a testing action in the test board; receiving a result data which is tested by the test board by the at least one relay module, and then transmitting the result data which is carried in a serial return signal to the software protector by the at least one relay module; packaging the result data by the software protector to form an encryption result data, and then converting the serial return signal into a return signal, and then transmitting the encryption result data to the test process module through the return signal; and storing the encryption result data by the test process module.