The formation mechanism of the chip in the process of cutting EA4T steel was explored by BTA deep hole drilling experiment. Influence on chip morphology was analyzed in different cases of cutting parameter by the way statistics chip morphology when used the BTA deep hole drilling EA4T steel. Based on this, a control scope of cutting parameter was gotten inversely by using the BTA deep hole drilling EA4T steel in the practical machining, which provided a theoretical basis in the practical machining. Experimental results show that BTA deep hole drilling is highly efficiency in terms of crumbs breaker, and desirable to obtain a C-shaped debris during the process of drilling the EA4T steel in a very large scope with different cutting speed or feeding rate.