Abstract: Aiming at the requirement of fast and nondestructive measurement of plane stress, a three-transmitters-three-receivers Rayleigh wave electromagnetic ultrasonic transducer (EMAT) was designed based on the principles of electromagnetic ultrasound. The structure and measurement system of the electromagnetic ultrasonic probe were introduced in details, and the formula for calculating plane stress based on the three-directions ultrasound velocity was modified. The plane stress can be measured when the probe was positioned once. A plane stress measurement experiment was performed in 5052 aluminum alloy by friction stir welding. And the measurement results were compared with the hole-drilling method, which verified the feasibility of the designed electromagnetic ultrasonic probe.