Thermal properties of feed and artificial experience have been generally considered, when adjusting the process parameters of hygrothermal treatment in the production of fish feed, including cooling and drying. Specific heat, thermal conductivity, and thermal diffusivity are the important thermal properties of fish feed. In this study, grass carp (adult fish) extruded feed was taken as the research object. The inversion algorithm was established to obtain the temperature distribution of feed using the adjoint equation. A test was also carried out using the self-developed heat conduction device and infrared thermal imager. When testing, the feed was quickly spread on the cast aluminum soaking plate, where the feed was closely arranged in a single layer, with a thickness of about 4 mm and a total of about 10 g. The infrared thermal images were captured for the feed layer surface and the upper surface on the cast aluminum soaking plate using the infrared thermal imager (accuracy±0.1℃). SmartView software was selected to process the infrared thermal images for the temperature-time data of the feed sample test surface (x=h) and heating surface (x=0), from the T-t data of heating surface x=0 and the feed sample test surface x=h. MATLAB software was selected first to solve the adjoint equation for the adjoint variables, then obtain the gradient value, and finally obtain specific heat c and thermal conductivity k. As such, the specific heat, thermal conductivity, and thermal diffusivity of feed were obtained, according to temperature distribution with the moisture content of 11%-17% and the temperature range of 20-80℃. The results show that the specific heat of grass carp extruded feed was 1.710-1.840 kJ/(kg•℃). Specific heat of feed increased significantly with the increase of temperature (P<0.05). When the moisture content increased from 11% to 17%, the specific heat of feed increased significantly (P<0.05), indicating a linear law. The thermal conductivity of grass carp extruded feed was 0.086-0.148 w/(m•K). When the temperature increased from 20℃ to 80℃, the thermal conductivity of grass carp extruded feed increased significantly (P<0.05). The effect of water content was also significant (P<0.05). The thermal diffusivity of feed ranged from 5.701 to 10.003 m2/s, depending significantly on temperature and moisture content (P<0.05). At the same time, the specific heat and thermal conductivity of feed were measured by Differential Scanning Calorimetry (DSC) and thermal characteristic analyzer, respectively, where the thermal diffusivity was calculated as the measured value. Before the test, the feed particles needed to be crushed. The inversion datum was taken as the calculated values. The linear fitting showed that R2 was equal or greater than 0.980, indicating the feasible determination of thermal characteristic parameters of fish extruded feed using the inversion. The finding can provide a new idea for the determination of the thermal properties of fish feed.