The field trials were conducted to study the effects of combined application of nitrogen and potassium on rice yield, K absorption, K utilization efficiency, K balance, K content in soil and the economic benefit of K fertilizer at 2 types of paddy soil in hilly regions of double-rice cropping system. Six plots were arranged, they were N1K0, N1K1, N1K2, N1K3, N2K0, N2K3 with combined application of four K levels, namely, K0, K1, K2 and K3, and two N levels (N1 and N2). K application rate of K0, K1, K2 and K3 in early rice and late rice were 0, 105, 150, 195 kg/hm2 (K2O，the same below) and 0.0, 136.5, 195.0, 253.5 kg/hm2, respectively. N application rate of N1, N2 in early rice and late rice were 150, 195 kg/hm2 (N, the same below) and 180, 234 kg/hm2, respectively. The results showed that K fertilizer application could obviously increase grain yields of early rice and late rice, especially for the late rice. Under N1 application level, the grain yield of N1K1 plot in early rice and N1K2 in late rice were the highest in reddish yellow soil, which increased by 5.1% and 13.9% compared with N1K0 plot, respectively. The grain yield of N1K3 plot in early rice and N1K2 in late rice were the highest in yellow clayey soil, which increased by 12.9% and 17.7% compared with N1K0 plot, respectively. K application was helpful to keep soil K balance and improve soil K level. Under N1 level, K balances of the experimental soils were deficient in N1K0 and N1K1 plots, and surplus in N1K2 and N1K3 plots in early rice, while, they were deficient in N1K0, N1K1 and N1K2, surplus in N1K3 in late rice. Compared with the initial level, the available K content in the two soils were increased in N1K2, N1K3 and N2K3 plots while decreased in N1K0, N1K1 and N2K0 plots after early rice and late rice were harvested. The economic profit of K application in reddish yellow soil was not significant in early rice but it was significant in late rice. The economic profit of grain in yellow soil was significant both in early and late rice. Therefore, it should pay attention to take K fertilizer suitable distribution under consideration in early rice and late rice for the improvement of rice yield, maintenance of soil potassium fertility and enhancement of grain economic benefit. The utilization principle should be recommended as less K application in early rice and more in late rice at double rice regimes in hilly regions of Hunan Province.