Underground fluid plays a crucial role in earthquake generation and precursor formation. Therefore,it is crucial to study underground fluid for the purpose to improve the earthquake prediction level. However,due to the lack of comprehensive understanding of the seismogenic environment and earthquake mechanism,it is nearly impossible to accurately predict the occurrence of earthquake based on the abnormal phenomena observed on the surface of earth. With the development of geophysics,geochemistry and tectonic geology studies,knowledge about underground fluid has been obtained. In this paper,based on the collection of relevant previous research results,we summarized several classical theoretical models,studied the main role of underground fluid played in the earthquake generation,and investigated the formation mechanism of underground fluid precursor in earthquake prediction. The research work has a reference significance for improving the level of earthquake prediction.