Abstract: Usually, the quality of seismic data of Xihu Depression is not quite well. The main reasons result from the characteristics of the seismic geological conditions in this area, such as development of thin sand-shale interbedding, no abrupt change or big bench between velocity and density, and difficult to form strong reflection interface, leading to development of multiples in seismic intervals. It is well-known that seismic multiples suppression is always a bottleneck in geophysics. To solve this bottleneck, VSP forward modeling is used to study the multiples forming mechanism of Xihu Depression in order to identify the main interfaces and horizons of multiples and provide the basis for suppression of multiples in digital processing. The dynamic laws and dynamic characteristics of multiples are studied on the basis of the data from actual drilling in Xihua Depression. Then VSP forward modeling is used to find the main horizons and interfaces of multiples and determine the relative strength of multiples and the types of main multiples affecting effective seismic waves. The research results indicate that all strong reflection interfaces in this area can produce multiples. The multiples that affect the quality of seismic imaging are compound multiples stacked with multiples from the different paths.