Diesel filter structure is roughly the same with the oil filter, there are two kinds of interchangeable and screw-mounted. But its work pressure and oil temperature requirements are much lower than the oil filter, and its filtration efficiency requirements are much higher than the oil filter. Diesel filter filter using filter paper, but also the use of felt or polymer materials. Diesel filter in addition to filtering the mechanical impurities in diesel, there is an important function is the water. The existence of water for the diesel engine oil supply system is extremely harmful, corrosion, wear, damage to the cylinder piston ring and even produce a cylinder phenomenon can also worsen the combustion process of diesel. Diesel filter system according to the different liquid density through the fluid flow control technology, the separation of water to achieve the effect of filtering water.