The problem of thermoacoustic Stirling engines (TASE) irreversity inside a regenerator is modeled and analyzed using entropy generation analysis in this paper. Assumption (long wave, short stack, small amplitude oscillation, boundary layer type flow, etc.) are made to enable simplification of the governing equations to achieve analytical solutions for velocity, temperature and pressure. Theoretical analysis and numerical calculation on entropy generation of the regenerator are done on the basis of considering irreversible qualities of both heat conduction and viscosity, the section distribution of entropy generation and the effect of some parameters on the average of entropy generation are discussed, and the optimization frequency is obtained.