A method for forming an ultra-shallow junction by boron plasma doping is disclosed. A substrate is placed in a pulse type electric field. A flowing carrying gas drives boron ions in a channel above the substrate, and then a negative pulse type voltage is applied so that the boron ions may uniformly enter into the substrate. Then a rapid annealing process is performed so as to be formed with an ultra-shallow junction on the substrate. In the present invention, by the boron plasma doping, an ultra-shallow junction is provided on a surface of the substrate. Therefore, after the next thermal process, the property of the element can be retained. A lower depth junction is acquired, and the diffusion in the horizontal direction is suppressed.