An air-gun source is the most commonly used excitation method in offshore seismic exploration.The excitation characteristics of an air-gun source affect seismic data quality.Far-field wavelet simulation is an important approach to study these characteristics.Compared to the measured wavelet,far-field wavelet simulation based on a traditional bubble-motion equation and ideal gas wavelet model has some disadvantages,such as a greater amplitude and smaller pulse attenuation velocity.Here,we start from the linear acoustic wave equation in the spherical coordinate system to deduce an improved,simpler bubble-motion equation and develop a Van der Waals gas wavelet model based on this equation.Unlike the existing methods,our method considers the high-pressure environment during actual excitation,heat exchange between the bubble and outside water,and change in the air flow at the muzzle.The results show that the far-field wavelet simulated using this model is closer to the measured wavelet than that of the ideal gas wavelet model.At the same time,our method has a more succinct equation and a higher calculation efficiency.