Abstract: A pot experiment with ¹⁵N tracing techniques was designed to study the effect of potassium application on nitrogen transfer, photosynthetic characteristics and nitrogen metabolism enzyme activities in two different growth stages of sweet potato. Results indicated that potassium application significantly increased the shoot ¹⁵N distribution rate. Compared with control, the ¹⁵N transfer rate of K₃ treatment increased by 76.2% and the total accumulation of ¹⁵N increased by 92.1% in tuber formation period. Different with tuber formation period, shoot ¹⁵N distribution rate decreased from 33.7% to 24.4%, but the root ¹⁵N distribution rate increased from 5.8% to 17% with the increase of K application in tuber rapid growth stage. Especially, root ¹⁵N accumulation of K₃ treatment was 3 times of the CK. During the two growth stages, nitrate reductase, glutamate dehydrogenase, glutamine synthetase, glutamate synthase and net photosynthetic rate all increased with the increase of K application. Stepwise regression analysis showed that nitrogen metabolism enzyme activities (nitrate reductase, glutamate dehydrogenase, glutamine synthetase, glutamate synthase) and P_n were the main factors to affect the ¹⁵N transfer and distribution of sweet potato (R₁=0.965,R₂=0.942). Path analysis showed that nitrate reductase and glutamate dehydrogenase activities were the key factors to influence ¹⁵N distribution to the shoot in tuber formation period, while glutamate dehydrogenase, glutamate synthase activities were the key factors to influence ¹⁵N distribution to the tuber in tuber rapid growth stage.