Fast， efficient， and reliable data transmission and processing are one of critical techniques to achieve smart digital relay protection. The fundamental technology requirements for data transmission of digital protection and related equipments are analyzed， and a new high-speed multi-channel synchronous serial hardware real-time exchange technique is proposed，which is based on multi field programmable gate array（FPGA） system for data sharing among CPU boards. Then the design and implementation of this technology in digital protection is introduced in detail. Meanwhile， the specific methods of hardware reliability design are presented. Finally， the digital protection equipment with this technique has been successfully applied in typical digital substation. In addition， this technique can be extended to applications of other digital equipment.