The prismatic Li-ion battery is a heterogeneous structure consisted of jelly-roll and aluminum shell. The thermal conductivity of the jelly-roll and the heat transfer coefficient between the jelly-roll and the shell are key parameters affecting heat dissipation. At present, there is no direct test method. It is proposed to use battery heat storage to construct a heat source, trigger unsteady heat transfer through the temperature change of the cooling surface. The thermal imaging is used to record the spatial distribution of the shell temperature along the heat transfer direction and its time evolution, and substitute it into the three-dimensional unsteady heat transfer inversion model. Meanwhile, core facing, longitudinal thermal conductivity, core and shell bottom, and maximum surface heat transfer coefficient are calculated. Experiment platform is constructed, tests carried out for two battery cells and three standard specimens. The relative standard deviation of the thermal conductivity test results of the two batteries cells is between 5% ~ 10% . The relative deviation of the results for three standard specimens are all below 5% . The method provides a new tool for experimental evaluation of thermal parameters for various non-uniform structures, for example the cylindrical battery cells.