Nitrogen is an essential nutrient for plant growth. However, the excessive use of nitrogen fertilizers not only increases production cost, but also has negative a impact on the environment. The purpose of this study was to quantify the source-sink characteristics and length of each growth stage in two potato varieties under different nitrogen application rates. This clarifies the source-sink coordination characteristics of the nitrogen-efficient variety and the source-sink coordination mechanisms of high nitrogen use efficiency (NUE). Field experiments were conducted in 2019, 2020, and 2021 using a split-plot design, with a nitrogen application rate of (0; 150 kg·ha⁻¹; 300 kg·ha⁻¹) as the main plot and variety (J, nitrogen-efficient variety Jizhang 12; Y, nitrogen-inefficient variety Youjia 70) as the subplot. The results showed that the yield and NUE of Jizhang 12 at 300 kg·ha⁻¹ were, on average, 90.73% and 75.15% higher than those of Youjia 70, respectively. The NUE and nitrogen utilization efficiency of Jizhang 12 increased on average, with decreasing N application at 68.66% and 24.53%, which were higher than those of Youjia 70 at 62.89% and 10.86%. Quantitative analysis of the source and sink showed that the Jizhang 12 had a higher source and sink capacity of 23.45 g and 51.85 g, respectively, and the maximum source and sink activity was on average 0.28 g·plant⁻¹·d⁻¹ and 1.47 g·plant⁻¹·d⁻¹ higher, and the growth period of the source and sink was on average 24 days and 7 days longer, respectively. On the basis of these results, the nitrogen-efficient varieties had a higher yield base and a smaller reduction in NUE with reduced N application. In terms of source-sink growth, N-efficient varieties lasted longer at the seedling and tuber initiation stages, when potatoes grew above ground and source organs grew for longer periods, providing a solid foundation for later sink growth, as evidenced by their higher source-sink activity, capacity, and growth time than N-inefficient varieties.