A fieldbus gateway using a virtual serial fieldbus port and a data transmission method thereof are provided. By receiving a fieldbus frame containing target data through a virtual serial fieldbus port connected to a source device or a target device via a fieldbus gateway and sending another fieldbus frame containing the target data via other fieldbus port to target devices or source devices, the system and the method can provide two or more remote devices to control one controlled device at the same time. The invention also achieves the effect of using one virtual serial fieldbus port to transmit data between multiple source devices and target devices concurrently.