The machining quality of bearing casing plays a decisive role in the service life and performance of the bearing. The hard cutting process method using polycrystalline diamond (PCD) tool cutting bearing casing has the advantages of high processing efficiency, high processing accuracy, green and no pollution. But the tool wear of PCD tool is very violent processing ferrous metal. To reduce the tool wear of PCD tool in hard turning of bearing rings, in this paper，a low-temperature carbon dioxide internal cooling assisted PCD tool cutting was used to suppress tool wear. A low temperature carbon dioxide cooling device was built to provide a stable low-temperature carbon dioxide jet for cutting tests. This cooling device includes a temperature sensor, quality sensor, pressure reduction valve and needle valve for temperature detection and flow regulation during testing. Then the cooling test of liquid carbon dioxide was carried out to analyze the cooling law of carbon dioxide. Carbon dioxide low-cooling test is divided into two parts:continuous cooling test and segmented cooling test. The cooling law of carbon dioxide under constant pressure (1.2 MPa ) during the continuous cooling test can be divided into three stages:initiation, stability and failure. The initiation stage of carbon dioxide amount is relatively sufficient, and the cooling temperature is minimally reduced to ?63 ℃. The cooling temperature then rises slowly for a period and remains stable, and the cooling phase begins to enter a stable phase, during which the cooling temperature almost no longer changes. Finally, the supply of carbon dioxide is insufficient, leading to the carbon dioxide inlet pressure can not remain stable, and the cooling effect is very poor. This stage is the failure stage. The flow rate in the stable stage is 1 000 g/min, and the cooling temperature remains unchanged at ?59 ℃. The segmented cooling test cooled carbon dioxide at different inlet pressures (0.8-1.6 MPa) and found that the lower the inlet pressure within the measured range, the lower the cooling temperature. Therefore, in the cryo-temperature cooling process, maintaining a small liquid carbon dioxide flow rate can get an ideal cooling effect. However, during the actual cooling experiment, when the inlet pressure of the internal cold vehicle blade is less than 0.8 MPa (the flow rate is less than 500 g/min), a large number of solid-state carbon dioxide particles will appear at the exit, which is easy to cause the pipeline blockage and the flow instability. Therefore, in the process of cryogenic cooling, keeping the inlet effect within 1-1.2 MPa can both obtain a stable cooling effect and avoid the waste of cryogenic coolant. Low-temperature cutting was carried out under different inlet pressures (0.8-1.4 MPa). The maximum reference cutting temperatures at 0.8 MPa, 1 MPa, 1.2 MPa and 1.4 MPa were ?41 ℃, ?28 ℃, ?30 ℃ and ?28 ℃, respectively. The roughness values of the machined surface were 0.071 μm, 0.074 μm, 0.109 μm and 0.129 μm, respectively. The maximum flank wear was 176.58 μm, 171.67 μm, 270.26 μm and 261.17 μm, respectively. When the inlet pressure was 0.8 MPa and 1 MPa, both the reference cutting temperature and the roughness value of the machined surface and the tool wear were at a low level. The low temperature cooling assisted PCD tool can effectively reduce the tool wear when hard turning bearing rings.