The invention relates to a robot compliance control system based on an EtherCAT bus, comprising a master station, a robot driver, a motor and a torque sensor. The master station is connected with the robot driver through an EtherCAT bus, and the robot driver is connected with the motor and the torque sensor. The master station superposes motor periodic data acquired by the robot driver and a set expected value and carries out impedance control, and outputs a reference torque value to the robot driver. The invention provides an EtherCAT bus-based modular robot compliance control method which has the advantages of strong real-time performance, high reliability, low cost and small size, and the method adapts to the requirements of the modern robots in executing contact work. The system and the method completely obey the EtherCAT protocol, and can be mixed with other EtherCAT drivers in use. Therefore, the application range of the method is increased.