The utility model relates to the technical field of gas turbines and in particular relates to a cooling mechanism of a transition section of a gas turbine combustion chamber and the gas turbine combustion chamber. The cooling mechanism of the transition section of the gas turbine combustion chamber comprises a transition section body, a pressure expander, a flow guide shell and an air entraining pipe, wherein the flow guide shell is arranged on the back of the transition section body to form a cooling channel; one end of the air entraining pipe is connected with the flow guide shell; the other end of the air entraining pipe is connected with air compressor stages; the compressed air in an air compressor is guided into the flow guide shell to form convection flow and cool the back of the transition section body, so that the cooling of the back of the transition section is improved; meanwhile, the air inflow of the pressure expander which is arranged under the abdomen part of the transition section body impacts the abdomen part of the transition section body to cool the abdomen part of the transition section body, so that the back of the transition section is effectively cooled and the transition section body is uniformly cooled, and thus the overall cooling effect of the transition section body is improved.