Abstract: Magnetic welding residual stress measurement method is a new method developed in the recent years. The key to the residual stress measurement is magnetic sensor design. It has large measurement error at the conventional sensor with two or four poles. In this paper, the sensor with nine poles could reduce the measurement error and was not needed need to rotate when the measurements were done. With the high permeability material and the electromagnetic simulation, the structure, shape and number of turns of the probe were optimized. The affecting factors were also analyzed. The nine-pole-sensor provided an advanced means for the fast residual stress measurement