Abstract: Pot culture and 14C tracer experimental methods etc. were used to determine the mechanism of K physiological efficiency (Dry matter or grain (kg) / K absorbed (kg)) difference in various rice varieties in relation to K application. Results showed that potassium application markedly increased the K content and K/N ratio in function leaves of late rice, stimulated the photosynthetic rate at different rice growth stages, enhanced the transportation of 14C-photosynthate from labelled leaf to panicle and other parts of rice plant and increased the accumulation of 14C-photosynthate in panicle. With normal level of K application, the K physiological efficiency of three rice varieties tested was in the order of 9194ZG66ZH904. Physiological features which may contribute the higher K physiological efficiency in the typical variety 9194 are as follows: 1) The higher K transportation and reutilization in rice plants and higher content of K in active leaves at rice grain filling stage; 2) The more sensitive response of photosynthesis to K application and lower rate of K requirement for maximum photosynthetic rate; 3) The favourable distribution of photosynthate in panicle, the higher harvest index and lower K requirement for optimum transportation and distribution of photosynthate.