The effects of various uncertain factors in the conduction path of a micro-expansion type heat switch on its thermal characteristics including OFF thermal resistance, ON thermal resistance and ON/OFF ratio were researched using parameter sensitivity analysis method. By comparing with the property experiment, the validity of heat switch finite element thermal model was verified. Based on the model, the relevance between thermal conductivity of structural components, thermal contact conductance of mating surfaces and OFF thermal resistance, ON thermal resistance and other thermal characteristics was analyzed. Then, the sensitivity of uncertain factors was classified by the absolute/relative variation of performance indexes. Research shows that the thermal conductivity of positioning shaft is the sensitive parameter about OFF thermal resistance and ON/OFF ratio, and the sensitivity indexes are 6.716 m0.5·K/W and 5.129 m0.5·K0.5/W0.5 respectively. The thermal contact conductance between cold side and disc is the sensitive parameter about ON thermal resistance, and the absolute variation and the sensitivity index are 1.865 K/W and 0.267 m·K/W respectively. The thermal contact conductances of other mating surfaces are the insensitive parameters about ON thermal resistance. Moreover, the shaft thermal facet-contact conductance is the sensitive parameter about OFF thermal resistance and ON/OFF ratio, and the absolute variations (sensitivity indexes) are 56.495 K/W (0.307 m·K/W) and 32.936 (0.235 m·K0.5/W0.5) respectively. These conclusions could provide the targeted reference for the structure-performance optimization of micro-expansion type heat switches.