The invention discloses a data processing method for low-frequency ultrasonic thoracic cavity imaging, which comprises the following steps: modeling through COMSOL, neglecting a spine and a heart in a model, combining two lungs into an ellipse with a long axis length of 0.15 m and a short axis length of 0.1 m, arranging a circle of annular skeletal muscle outside the ellipse of the lungs, uniformly placing 12 ultrasonic transducers around the exterior of the skeletal muscle, the material is set to be PZT-5H; one transducer is used as a sound source Sk which needs to be identified, seven transducers which directly face each other are used as receiving array elements, and signals received by the array elements are subjected to sound source identification processing by using a multi-signal classification (Multiple Signal Characterization,MUSIC) algorithm; a model is established through COMSOL, and a data processing technology applied to the field of low-frequency ultrasonic thoracic cavity imaging is creatively discovered according to a cyclic transmitting-receiving mode of one transmitting and seven receiving. According to the technology, the signal-to-noise ratio of array receiving data can be improved, and the mean square error of the data is reduced.