Puccinellia tenuiflora, a perennial gramineal plant, which can grow in alkalized soil after artificial planting, and it has been emploied in the biological harness of alkalized soil. The salt entered Puccinellia tenuiflora can be eliminated via stoma or along with wax secretion to leaf surface. There is high content of Na and K and other elements on leaf surface when it grows normally, and content of Na and K on leaf surface shows regular changes under the Na2CO3 stress of different concentrations. However, how the Na and K content alternate and the function of maintaining the ion balance and osmotic adjustment in mesophyll cells under Na2CO3 stress are not completely understood? The K and Na level in epidermis and mesophyll cells of Puccinellia tenuiflora seedling leaves under the Na2CO3 stress of different concentrations was investigated by using transmission electron microscopy, environmental scanning electron microscopy, and X-ray electron probe microanalysis. Under the same stress intensity, the relative content of Na in either cell wall or vacuole of epidermis and mesophyll cells was higher than that in cytoplasm, and the K level was significantly higher than Na in the same location. The changes of Na content in cell wall and vacuole had the same range. When Na2CO3 concentration was lower than 0.1 mol L-1, the relative content of K was higher than that of Na under the same stress intensity, so the K / Na ratio in cytoplasm was relatively high. Although plenty of Na was dispersed into cell wall and vacuole, the relative content of Na in cytoplasm was still elevated along with Na2CO3 stress. These data confirmed that the ability of Puccinellia tenuiflora to maintain the higher K / Na ratio in cytoplasm is finite, and implied that Puccinellia tenuiflora, as salt tolerant plant growing in salt and alkali environment, its cytoplasmic Na may partially substitutes for K and takes the function of K to some extent.