Abstract: In the offshore seafloor in-situ detection, the use of multi-array focused technology can compensate for the inherent deficiency of the acoustic parametric array to produce a strong difference frequency energy, but the high energy of the primary frequency signal at the acoustic focal point can lead to amplitude clipping in the receiving system, which causes waveform distortion. Transducers are also susceptible to damage during sound field measurements. In this paper, a dual-element focused parametric array with its acoustic focus located in the far difference-frequency sound field is taken as a research object. Based on KZK (Khokhlov -Zabolotskaya-Kuznetsov) equation and Berktay's envelope self demodulation theory, the way to suppress the primary frequency sound field by changing the transmitting signal without affecting the difference frequency sound field is proposed. The results show that, in contrast to the case where two arrays emit amplitude modulated signals in the same phase, when the two emitting signals are in opposite phases, the primary frequency sound pressure level (SPL) decreases along the acoustic axis with a 13.2 dB reduction at the acoustic focal point, while the difference frequency sound field remains unchanged.