The oil leakage of Rexroth variable plunger pump is mainly caused by the damage of internal parts, and the impact caused by different damaged parts is also different. A common type of damage is damage to the main shaft oil seal or defective shaft. In addition, excessive internal leakage will cause the pressure increase at the oil seal to damage the oil seal. Excessively thin and long drain pipes will also cause oil leakage at the seal. Poor welding will also cause oil leakage during mechanical production, but this is very rare.