The invention provides an alternating-current signal acquisition board for a flexible alternating-current transmission device. The alternating-current signal acquisition board comprises a signal acquisition module, an AD (analog to digital) conversion module, a CPLD (complex programmable logic device) module, an EtherCAT (Ethernet for control automation technology) slave station module and an input-output module, the CPLD module is connected with and controls the AD conversion module and the EtherCAT slave station module, the signal acquisition module acquires voltage and current of a main circuit of the flexible alternating-current transmission device and converts the voltage and the current into alternating-current analog signals, the AD conversion module converts low-voltage analog signals into digital signals, and the CPLD module reads the digital signals generated by conversion of the AD conversion module. One end of the EtherCAT slave station module is connected with the CPLD module while the other end thereof is connected with an EtherCAT bus outside the alternating-current signal acquisition board to transmit the digital signals sent by the CPLD module to the EtherCAT bus. The alternating-current signal acquisition board for the flexible alternating-current transmission device adopts an independent AD conversion chip, and can sample alternating-current signals by 16-bit high precision, and influences of common-mode interference on sampled signals are reduced by adopting a differential input mode.