The invention provides a fish mouth sealing structure between a turbine rotor and stator of a gas turbine. The fish mouth sealing structure is formed by a turbine guider inner ring outlet mounting edge, a turbine rotor inner ring front edge wall face and an auxiliary fish mouth sealing conic barrel in a cooperation manner. The turbine guider inner ring outlet mounting edge is a simple annular flatplate, and bosses are circumferentially and evenly distributed on one side of the turbine guider inner ring outlet mounting edge. A vertical ring plate and a horizontal ring plate are arranged on themaximum radius portion of the auxiliary fish mouth sealing conic barrel, grooves are formed in the vertical ring plate to cooperate with the bosses of the turbine guider inner ring outlet mounting edge, a turbine guider is prevented from rotating circumferentially, and the minimum radius portion of the auxiliary fish mouth sealing conic barrel is fixed to a static component through a bolt. High-pressure sealing air flows out to a main channel through the fish mouth sealing structure, and high-temperature gas is prevented from intruding inside. By means of the sealing structure, the sealing effect between the high-pressure turbine rotor and guider is improved, the processing difficulty of the sealing structure is reduced, heat stress of an inner ring rear mounting edge of the high-pressureturbine guider is also reduced, and therefore the performance and competitive power of an engine are improved.