The multi-axis servo linkage sees more and more applications in the industrial field, and its synchronization is an urgent issue. The introduction of the EtherCAT (Ethernet for Control Automation Technology) into the multi-axis servo motion system could improve the synchronization of the system. In order to enhance the performance of a multi-axis servo motion system with the EtherCAT, this paper first discusses the EtherCAT's basic communication theory, and the basic structure of a multi-axis servo motion controller system, based on the EtherCAT, and the theory of the slave. Then, we analyze the synchronization of the EtherCAT by calculating the delay, the compensating offset and the compensating drift. At last, an experiment is carried out, which shows that, the EtherCAT's synchronization can satisfy the requirements of the multi-axis motion controller system very well.