Because of the high efficiency and energy saving characteristics of the four-level BB2 type oil pump, the two-level BB2 type oil pump at home and abroad is optimized into the four-level structure to study its field characteristic flow and verify its effectiveness and rationality.We used computational fluid mechanics to simulate flow field,and found that the pressure distribution of the first and secondary impeller inlet to the outlet was relatively uniform, with obvious pressure gradient,and the flow field stability of the secondary impeller was relatively poor;In addition, we found that the flow in the passage was evenly distributed, and the velocity direction was basically the same as the rotation direction,and the velocity in the secondary impeller was greater than that in the first stage impeller, and the flow velocity was lower than that of the back flow, and the velocity reversal occurs at the outlet of the impeller.According to the experimental data,the flow, head, efficiency and cavitation residue of BB2 type oil pump with four-level structure all conform to the national standards and reach the practical effect of more efficient energy saving.