The cleanliness of the oil pump housing has an important influence on the overall performance of transmission lubrication system. Due to the complex structure of the oil pump housing, it is difficult to achieve the cleanliness requirements by using general cleaning methods. Combined with high pressure water jet cleaning technology and precision cleaning technology, not only the regular parts can be cleaned, but also the holes, gaps and other parts can be cleaned. The experimental results show that by using the proposed cleaning technology, the cleanliness of the oil pump housing can be greatly improved and the product performance requirements can be met.