Abstract: The research on coal breaking mechanism by high-pressure water jet can provide theoretical basis for water jet equipment manufacturing and construction technology research. In this paper, based on the investigation of a large number of related literatures at home and abroad, we summarized the relevant theories of coal breaking mechanism by high pressure water jet. From the perspective of the structure of water jet and mechanical properties of coal, this paper introduces the stress wave theory of crushing, quasi-static elastic fracture theory, the theory of cavitation and broken and crack propagation mechanism of broken coal at all stages about crushing theory researches. In view of the applicability and limitations of various current coal breaking theories, it is suggested that further research can be carried out from three directions: improving the coal breaking mechanism of water jet, two-phase jet and new jet mode.