<p>Relying solely on experience and trial cutting to determine the range of main process parameters for deep hole machining in order to control the cutting shape is time-consuming, laborious, and costly. This article simplifies chips into three-dimensional curved beams with rectangular cross sections and theoretically analyzes the stress states at different stages of their formation process, clarifying the mechanical causes of the three-dimensional shape of chips. A self-constructed deep hole drilling device with internal chip removal was used to test deep hole machining of <i>φ</i> 30 mm on 50^# steel. By calculating the chip breakage rate and compression rate of each tooth, it was determined that the values of chip breakage rate and compression rate of small-diameter deep hole drilling are less than 10, which are key quantitative indexes for controlling the chip morphology to realize good chip breakage and chip removal. By using scanning electron microscopy, the microscopic morphology characteristics of the chip fracture surfaces of each tooth under different process parameter combinations were analyzed in detail, and the effects of feed rate and speed on chip morphology were explored, providing data reference for the rational selection of process parameters for small-diameter inner chip removal deep hole machining.</p>