A sensor device, comprising two symmetrically disposed sonolucent wedges (5), and a connecting piece for fixedly connecting the two sonolucent wedges (5); the upper surfaces of the sonolucent wedges (5) are provided with inclined planes; installation holes are formed on the inclined planes; transducers (3) are installed in respective installation holes; one transducer (3) is used to generate ultrasonic waves, and the other transducer (3) is used to receive the ultrasonic waves generated by the previous transducer (3). The residual stress detection system comprises a sensor device, an ultrasonic transmission card, and a data acquisition card.