he problems of the efficiency loss of PP1209 solvent sump mechanical seals and shortness of lifespan concerning mechanical seal were researched. The efficiency loss of mechanical seals was analyzed，the reason of fault was obtained，and seal product as well as reforming plan were put forward. Application practice indicates that the leakage quantity is obviously reduced comparing with that of original seal and the service life is prolonged correspondingly via running after improvement and reassembling onto the machine，to keep the equipment run in normal performance for long term，and save the cost and promoting economic benefit.