Abstract: The potato (Solanum tuberosum L.) is an important grain and vegetable crop. Global warming affects its growth and production owing to its high temperature sensitivity. Investigating the physiological differences between heat-tolerant and heat-sensitive resources can help rationalize the mechanism of high-temperature resistance in potatoes. The parameters related to the morphology and photosynthesis of the heat-tolerant line ‘Dian 187’ (D187) and the heat-sensitive cultivar ‘Qingshu 9’ (QS9) were measured and analyzed after two weeks of high-temperature stress at 30 ℃. Under high-temperature stress, the plant height and internode length were increased, the leaves were upright, the length and area of leaves were reduced, and the plant architecture was more compact. The extent of change in the leaf number and bend angle in D187 was greater than that in QS9. The high-temperature affected potato net photosynthetic rate, water use efficiency, maximum net photosynthetic rate, apparent quantum yield, carboxylation efficiency, maximum carboxylation rate, and maximum electron transport rate, which were lower in QS9 than those in D187 under high-temperature stress. Furthermore, D187 had a lower light compensation point and dark respiration rate than the heat-sensitive cultivar (QS9), and as a result of its strong adaptability, the number of indexes with phenotypic plasticity index exceeding 0.5 in D187 was more than that in QS9. The mean phenotypic plasticity index of morphology, photosynthesis, and yield was 0.448 in D187, which was higher than that in QS9 (0.418). Furthermore, under high-temperature stress, the ability to absorb CO₂ and low-concentration CO₂ utilization were weakened, along with the acceleration of water loss and the reduction of water use efficiency in potato plants. Consequently, respiratory consumption increased, and the regeneration abilities of ribulose 1,5-diphosphate (RuBP) and chlorophyll fluorescence parameters were reduced in the dark. In contrast, chlorophyll fluorescence parameters increased under light, and the utilization ability of limited light was also enhanced. Differences in morphology and photosynthetic self-adaptation abilities are the main reasons for the difference in high-temperature resistance between heat-tolerant and heat-sensitive resources, which will help clarify the mechanism of high-temperature adaptability in potato plants and provide references for the selection of cultivars with high-temperature resistance and innovation in cultivation techniques.