It is an expectation of most of the numerical control products manufacturer that have a powerful controller with whole won intellectual property and without restriction from other companies. The paper introduces a new type of motion controller that based on ARM and EtherCAT field bus. It concludes the analysis and porting method of the EtherCAT soft master source code, and how to modify the driver of dm9000 to make EtherCAT master works correctly. It also gives an example to confirm the reliability of the controller. Since ARM has an open architecture, EtherCAT soft master does not depend on any special hardware card, and Linux OS is an open source system, this controller has open and flexible characteristic both on hardware and software.