The internal mechanical structure composition of the medium constant pressure plugging type automatic oil pollution detector and the specific process of oil pollution detection were introduced. The FLUENT fluid analysis software was used to simulate the pressure of the pipeline system between the sampling cylinder joint and the filter of the oil pollution detector and the test cylinder interface, and the results were analyzed. The results show that the pressure loss in the oil circuit system is small, which is within a reasonable range, so the influence on the oil pollution degree detection is small, the design reasonableness has been proved.