The invention discloses a sampling system based on series connection of optical fibers. The sampling system includes a plurality of sampling board cards, and the sampling board cards and sampling receiving board cards are in end-to-end series connection through the optical fibers to form a bidirectional ring network. Sampled data messages of the sampling board cards can be transmitted in both directions in the optical fiber ring network. The failure of any one board card does not affect other board cards to send and receive the messages. The system can form two completely independent A and B ring networks, and the redundant structures of the A and B networks can improve the reliability of the sampling system. The sampling system of an optical fiber serial connection structure can effectively reduce the use number of the optical fibers, so that not only is the complexity of system networking reduced but also the cost is effectively reduced. Each sampling and receiving board card can beautomatically synchronized to allow sampling board card MAC addresses of the messages to be sent in the ring networks, and each sampling and receiving board card only needs to configure the sampling board MAC address which needs to be received. The dependence between the sampling board cards is reduced, and later upgrading and maintenance are facilitated. The sampling system can achieve simultaneous sampling of all the sampling board cards.