Abstract: In this paper, for a double-acting Stirling heat engine, the thermal solution of the internal gas parcels is carried out through SAGE calculation, Runge-Kutta method, and linear interpolation post-processing processes, and finally the thermal solution results are converted from the Eulerian view to the Lagrangian view. The research results show that each gas parcel in the Stirling heat engine regenerator operates independently in different thermal processes, and the gas parcels relay with each other, realizing the macro engine thermal power conversion function. The envelope of the thermal cycle is similar to the combination of two isobaric processes and two isothermal processes. At the same time, this paper studies the operation mechanism and thermal process of the actual model of the gas parcel and verifies the relationship between the Stirling cycle and the generalized Carnot cycle from a numerical point of view, which provides a theoretical basis for the design and analysis of the Stirling heat engine.