The invention provides a stress measurement primary stress separation method and device based on an ultrasonic surface wave and belongs to methods and devices of measuring the surface stresses of materials. The separation device comprises an ultrasonic transducer, an ultrasonic pulse transmission receiver, a sampling processing system and an analysis system. The output end of the ultrasonic transducer is connected with the input end of the ultrasonic pulse transmission receiver. The output end of the ultrasonic pulse transmission receiver is connected with the input end of the sampling processing system. The output end of the sampling processing system is connected with the analysis system through a digital oscilloscope. The working stress and the residual stress on the surface of an object are measured through the surface wave. In addition, the principle stress separation method is provided. Replication experiments of two-dimension stress measurement achieve surface wave lossless detection of two-dimension plane stress, a demonstration objet is A3 steel, the engineering application value is high, the experiment precision is high, and the stress measurement principle stress separation method and device are suitable for engineering detection. Through the advantages of ultrasound, lossless detection can be conduced on the single-point multi-dimension stress at any position.