The diesel filter can effectively block the dust and moisture in the diesel oil, and can effectively extend the service life of the fuel injection pump, diesel nozzle and other filter components. Large and small oil droplets, large oil droplets through the oil-gas separator easy to separate, and small oil droplets (suspended oil particles) must be through the oil-gas separation filter micron-level glass fiber layer filtration. When the diameter and thickness of glass fiber are correctly selected, the filter media can intercept, diffuse and polymerize the oil mist in the gas, and the effect can reach the best. Small oil droplets quickly gather into large oil droplets, in the pneumatic and gravity driven through the filter layer, accumulation in the bottom of the filter, and then return through the back of the oil pipe at the bottom recess of the filter inlet lubrication system, so that the compressor discharge more pure, oil-free Compressed air.