The experimental aimed at the contents of Fe, Mn, Cu and Zn in the seeds of wheat, soybean and maize, and the contents of Fe, Mn, Cu and Zn in different forms in soil, and the data were obtained from 42 experimental plots in the Three River Plain. This paper illustrated the bio-availability of Fe, Mn, Cu and Zn in different forms in soil in order to find a scientific method for application of trace elements in the Three River Plain. The correlated analyses showed that the contents of available, exchangeable and organic Fe, Mn, Cu and Zn in soil had significant or very significant positive correlations with those in the seeds of wheat, soybean and maize. The results of path analyses showed that the effect of exchangeable forms on available Fe, Mn, Cu and Zn was most, followed by the organic form. The oxide bound Fe, Cu to available Fe, Cu and carbonate bound Mn, Zn to available Mn, Zn showed positive effect, but residual Fe, Cu to available Fe, Cu and oxide bound Mn to available Mn show negative effect.