Abstract: A composite structure sensor which was composed of Al2O3-C refractories containing 20% and 30% graphite was proposed to overcome the problem of slow response speed of continuous temperature-measuring system for liquid steel. To study the effectiveness and feasibility of the proposed sensor, a finite element method was used to investigate the heat transfer and transient thermal stress during start process of teeming for this sensor. The results indicated that the maximum thermal stress occurs at the inside wall of the sensor's body and closes to the junction between body and measuring section. The maximum stress is about 4 MPa, which is smaller than the strength of sensor. The adoption of composite structure can improve response rate obviously. To reach 98% of actual temperature, the proposed composite structure sensor needs only half of the time that the original sensor needs.