Airgun has been used as an active source to generate seismic waves in on‐land reservoirs by releasing high pressure air beneath the water surface. There are significant differences in signal energy and frequency given different airgun placement depths. In this article, we compared and analyzed the signal characteristics of airgun placed at different depths in the Qilian Mountain in Gansu Province. Results show that both the amplitude (energy) and the dominant frequency of the airgun signal increased with increasing placement depths. Within the tested depth range, we found that the optimum airgun placement depth was 30 m and the dominant frequency was 3–13 Hz. Further implementation of these findings can help improve the extraction accuracy of the weak signals in the observation system.