By analyzing several environmental properties of soil in the riparian zone, particularly, our studies on nitrogen and phosphorus content of Solidago Canadensis L. each growth period one year, revealed mechanism of how S. Canadensis L. successfully invaded in riparian zone. Research results show that:Nitrogen content, in the upper and lower soil area respectively, is 1.22mg/g and 0.96mg/g. In comparison, phosphorus content in the upper soil is 0.59mg/g, in the lower one is 0.55mg/g, which are lower than national average soil nitrogen and phosphorus content. In addition, obvious interannual variation was not observed and N/P average we measured was apparently low and decreased with the seasons changed. Each part of the S. Canadensis L. nitrogen and phosphorus content is leaf>stem>root. Comparing with other herbs, the nitrogen content of S. Canadensis L. is much low, however, the phosphorus content is obviously on the high side. Along with the change of vegetation growth, nitrogen and phosphorus content of each part in the plant demonstrates a trend of decreasing at beginning then increases at the end. N/P of S. Canadensis L. ranging from 2.25 to 4.75, is significantly lower than the other herbs. Plants of S. Canadensis L. has a high phosphorus content and a lack of nitrogen in the soil so as to its growth was limited by N. By analyzing nitrogen and phosphorus in plant stem, leaf, root element and the N/P correlation shows that the phosphorus content in the stem and leaf and N/P has significant negative correlation (P<0.05), while nitrogen content in the root and the N/P has a significant positive correlation (P<0.01) which illustrates the phosphorus dominated the growth of plants and nitrogen dominated the underground part. With a grave shortage of soil nitrogen content and phosphorus content obviously lower in the study, the nitrogen content in the plant of S. Canadensis L. is only slightly lower than other herbaceous plants and the phosphorus content is significantly higher than that of other plants. It could be probably that its ability of absorption and accumulation nitrogen and phosphorus is much higher than other herbs, which might be the mechanism of S. canadensis invaded in the special environment of riparian zone successfully.