The invention relates to a testing tool for an automobile air compressor, in particular to a tool for testing air carry over of an air compressor. The tool for testing the oil carry over of the air compressor includes a joint, wherein a rear cylinder of the joint is fixed in the inner ring of a bearing, the outer ring of the bearing is fixed in a bearing bush, a supporting frame is installed between the bearing bush and a supporting seat, and a filter paper seat is installed at the back of the supporting seat. A gap is formed in the supporting frame. Threads, matched with the vent of the air compressor, are formed in the front cylinder of the joint. The middle portion of the joint is a hexagonal prism. The inner ring of the supporting seat is stair-stepping. The filter paper seat is a stair-stepping boss which is matched with the inner ring. Clamping grooves are formed in the supporting seat. Protrusions are arranged on the filter paper seat. The tool for testing the oil carry over of the air compressor fills the market blank, changes the traditional handheld test mode and the simple and crude testing tools and is simple in structure, convenient to carry and use and reliable in test result.