The invention discloses a video optical multiplexer, a video transmission system and a method for controlling video signal transmission. The video transmission system comprises an upper computer, a network management terminal and the video optical multiplexer serving as master equipment and slave equipment; the upper computer sends video transmission configuration information to the video opticalmultiplexer serving as the master equipment via a gateway terminal for indicating a dynamic regulation transmission direction and the number of transmission ports corresponding to the transmission direction; the master equipment regulates the transmission direction of a corresponding video interface and the number of the corresponding transmission ports according to the video transmission configuration information, and sends the video transmission configuration information to the slave equipment; the slave equipment regulates the transmission direction of the corresponding video interface according to the video transmission configuration information; the transmission direction of the video interface of the slave equipment is opposite to that of the video interface of the master equipment;and the number of the transmission ports corresponding to the master equipment is set. The transmission direction and the number of the transmission ports can be flexibly configured.