The Stirling cycle cryocoolers are usually used for HPGe detectors cooling in γ- radiation portable spectrometers for field applications. The cooling of large size germanium detectors up to cryogenic temperatures by application of low-power cryocoolers makes the topical task of the thermal losses analysis. The equivalent thermal model of detector unit and Stirling cryocooler created by thermoelectric analogies is presented. Thermal modeling is used for analysis and optimization of cooling path from cryocooler to detector can for thermal losses reduction. The calculated cooldown curves of the detector unit as the transition process for the proposed model are compared to the experimental results. It is shown that the proposed model allows simulate the cooldown processes for HPGe detector with accuracy sufficient for the practical applications. The temperature distribution diagrams for the thermal joints obtained by SolidWorks Simulation are presented.