Through analyzing the near-field hydrophone records of the air-gun experiment in the Jiemian reservoir，Fujian，we study the time-frequency characteristic of air-gun source wavelet and the influence of gun depth and firing pressure，and explain the process of bubble oscillation based on the Johnson(1994)bubble model. The data analysis shows that: (1)Air-gun wavelet is composed of main pulse and bubble pulse. Main pulse，which is of large amplitude，short duration and wide frequency band，is usually used in shallow exploration. Bubble pulse，which is concentrated in low-frequency band，is usually used in deep exploration with deep vertical penetration and far horizontal propagation. (2)With gun depth increasing，the variation of main pulse amplitude is very small，bubble pulse amplitude and the dominant frequency increase，peak-bubble ratio and bubble period decrease. When gun depth is 10m，main pulse amplitude and peak-bubble ratio are maximum，which is suitable in shallow exploration；when gun depth is 25m，bubble pulse amplitude is large，and peak-bubble ratio is minimum，which is suitable in deep exploration. (3)With firing pressure increasing，main pulse amplitude，bubble pulse amplitude，peak-bubble ratio，and bubble period increase，the dominant frequency decreases.