Abstract: Based on the mechanism of photoacoustic nonlinear mixed-frequencies, a method of generating nonlinear mixed-frequency signals by separating exciting light source from heating light source in space is studied in this paper. Furthermore, the contribution of two sources to the nonlinear mixed-frequency signals in acoustics and thermology is discussed by studying the change of the corresponding nonlinear side lobe signal with the position of the laser source. In the experiment, keeping one laser beam at the crack and moving another laser beam near the crack, the change of the amplitude of nonlinear mixed-frequency signals with the position of the moving light source was studied. The experimental results show that there is a phenomenon of nonlinear mixed-frequencies in the scanning laser in the range of about six times the laser spot diameter from the crack. Furthermore, the heating light source is irradiating the crack, and the excitation light source is moved to the area where the mixed-frequency signals cannot be produced, so the nonlinear mixed-frequency signals cannot be produced by compensating the power of the heating light source. This phenomenon shows that, on the basis of the generation mechanism of photoacoustic nonlinear mixed-frequencies, it is necessary to further consider the high-frequency sound wave of the excitation source and the amplitude change of the excitation source in the generation of the nonlinear mixed-frequency signals.