A communication system and a communication method for one-way transmission are provided. The communication method includes: transmitting a filtering rule to a programmable logic device by a server; receiving a signal and obtaining data from the signal by the server; packing the data to generate at least one data packet by the server; transmitting the at least one data packet to the programmable logic device by the server; and determining, according to the filtering rule, whether to output the at least one data packet by the programmable logic device.