The invention relates to a base band data transmission installation and its frame synchronization method. It includes framing machine, serializer, deserialiser, deframing machine, synchronizing frame inserting controller. The serializer and the deserialiser are physically connected by low pressure high speed differential line. The framing machine is used to form the user data to user data frame with the same length. Meanwhile, the synchronizing frame inserting controller inserted synchronizing frame to free frame position periodically, the user data frame and the synchronizing frame are formed to parallel data. The serializer transforms the parallel data after framing to serial data by coding, and transforms to differential signal and transmits out by the low pressure high speed differential line. After the deserialiser transforms the received differential signal to single end signal, the serial data will be transformed to parallel data. The deframing machine finds the frame boundary according to the frame synchronization information contained in the received parallel data, then, each of the received frame data will be distributed to the after stage unit to use. The advantage of the installation and method of the invention is that the band width took up is small, the transmission efficiency is high, and the cost of the frame synchronization is reduced.