To minish the friction resistance of moving parts in engine, relieve the parts friction , the engine oil will be sent to the cover of everymoving parts, to make a lubricating form . The engine oil is including colloid, impurity, water and additive, and in the engine working period, there’ll be also metal abrasive dust, air impurity and engine oil oxid, it will cause the engine oil impurity to be more. If the engine oil isn’t filtered and into the oilway directly, it’ll cause  the oil impurity to the cover of moving parts, to accelerate the parts friction and reduce the engine operation life. The oil filter is to filter colloid, impurity, water of engine oil, to send clean oil to every moving parts.every moving parts.