A system for identifying the position of a marker for orthopedic surgery, the system comprising: a sensor part for installation near a surgical site and on an orthopedic surgical robot , the sensor part including an optical marker (11; 12; 13) and a sensor (21; 22; 23); a first position detecting part for detecting the position of the optical marker (11; 12; 13); a second position detecting part for detecting the position of the sensor (21; 22; 23); and a control part for setting either the first position detecting part or the second position detecting part to main sensor and the other to auxiliary sensor, and for tracking position and posture of the sensor part based on position signals detected by the main sensor and the auxiliary sensor; wherein the control part comprises a sensor-failure decision part for determining failure of the first position detecting part and the second position detecting part , and a sensor-failure alert part connected to the sensor-failure decision part for displaying a sensor-failure notification message when sensor-failure occurs; wherein the control part is configured to generate a robot decelerating signal and to send it to the orthopedic surgical robot when failure of one of the first position detecting part and the second position detecting part occurs; wherein the sensor-failure decision part is configured to set the position detecting part set as the auxiliary sensor to the main sensor when failure of the position detecting part set as the main sensor occurs and the position detecting part set as the auxiliary sensor operates normally; wherein the control part is configured to recognize the position and the posture of the sensor part based on only the position signals of the position detecting part changed to the main sensor when failure of the position detecting part set as the main sensor occurs and the position detecting part set as the auxiliary sensor operates normally; and wherein the first position detecting part is an optical tracking sensor. a sensor part for installation near a surgical site and on an orthopedic surgical robot , the sensor part including an optical marker (11; 12; 13) and a sensor (21; 22; 23); a first position detecting part for detecting the position of the optical marker (11; 12; 13); a second position detecting part for detecting the position of the sensor (21; 22; 23); and a control part for setting either the first position detecting part or the second position detecting part to main sensor and the other to auxiliary sensor, and for tracking position and posture of the sensor part based on position signals detected by the main sensor and the auxiliary sensor; wherein the control part comprises a sensor-failure decision part for determining failure of the first position detecting part and the second position detecting part , and a sensor-failure alert part connected to the sensor-failure decision part for displaying a sensor-failure notification message when sensor-failure occurs; wherein the control part is configured to generate a robot decelerating signal and to send it to the orthopedic surgical robot when failure of one of the first position detecting part and the second position detecting part occurs; wherein the sensor-failure decision part is configured to set the position detecting part set as the auxiliary sensor to the main sensor when failure of the position detecting part set as the main sensor occurs and the position detecting part set as the auxiliary sensor operates normally; wherein the control part is configured to recognize the position and the posture of the sensor part based on only the position signals of the position detecting part changed to the main sensor when failure of the position detecting part set as the main sensor occurs and the position detecting part set as the auxiliary sensor operates normally; and wherein the first position detecting part is an optical tracking sensor. <EOS>