Abstract: Sulige gas field is characterized by low pressure, low permeability, and low abundance. It is a lithologic reservoir dominated by fluvial sand bodies, with widely pool distribution, flat structure (the dip angle is less than 1°), but no development of faults. So it is suitable for the application of broadband excitation techniques. Surface structure of the northern area of the gas field varies a lot horizontally. Test shows that single shot energy, frequency, signal-to-noise ratio of the northern area is directly related to whether they are excited below the free surface. Based on reinforcing study on the correlation between the surface structure and free surface of the area in recent years, to design the excitation depth no longer relies on the high-speed layer top, but on the correlation between the free surface and the spin-down layer top and high-speed layer top, and the surface speed. Raw data featuring in high consistency of energy with frequency and broad band are obtained, and better seismic and geologic results are acquired

Key words: broadband excitation, free surface, excitation, Sulige