Abstract: To study the decomposition and transferring rate of straw, the 14C traced straw was used in labor and field experiments. The preliminary results are as follows:( 1 ) Decomposition rate of straw depends mainly on the C/N ratio. After straw applied into soil, the population of microorganism increases rapidly, especially bacteria.( 2 ) During its decomposition, the straw changes at first into the non-structure substances. Most of these non-structure substances transfers then into fulvic acfd and afterwards humic acid. The dico-mposed substances can renew soil humus. The procedure takes place at the functional groups of humus surface and the fraction of the molecules. The non-structure substance can cross link with a single humic acid molecule. Under certain conditions the cross-linked molecule can enter into the kernel of humus molecule. The transformation and re-distribution of the single component of humic acid in soil is only close related with exchange reaction of functional groups of humus.( 3 ) Clay minerals can adsorb humic acid selectively. Preference of this selective adsorption is given to the low molecule humic acids.