The invention relates to a network isolation system and a data transmission method thereof. The network isolation system comprises a transmission controller, a plurality of first isolation devices and a receiving controller, wherein the transmission controller is used for processing the transmission data and forming multiple paths of data transmitted in parallel; the first isolation devices are used for transmitting required data transmitted in parallel; and the receiving controller is used for receiving and processing the data transmitted in parallel so as to obtain the data to be transmitted before the transmission controller processes. The network isolation system and the data transmission method thereof of the invention can improve data transmission rate and stability.