Ammonium assimilation is a very important process to transform inorganic nitrogen into organic nitrogen for plants. The course of ammonium assimilation, the crucial enzymes and the molecular mechanism of ammonium assimilation in woody plant were summarized in this paper. The research progress on the location of key enzymes, biochemical properties, gene expression and regulation during amino assimilation in woody plants were mainly discussed. The prospect on molecular biology mechanism of amino assimilation increasing the efficiency of available nitrogen, accelerating plants growth and so on were also discussed in the paper.