Abstract: The internal die is used as one of the basic operational tools for cold-drawing of steel tubes. As a primitive processing technique,the conventional process of carbonization-chromium plating of the internal die metal surface is mostly employed by relevant domestic manufacturers,producing serious environmental pollution as caused by waste liquid discharge. Described here is a newly-developed process involving the after-machining solid boronization of the said internal die,which not only enhance the service span and productivity of the die,and reduce the costs,but also diminish the environmental pollution.