Abstract: The L-8900 high-speed auto amino acid analyzer was bought in 2008, the long term use and without proper maintenance resulted in the overpressure problem of pump 1 so that the analyzer cannot run normally. The replacement of the linear filter and back wash of analytical column did not work. Finally, the refill of the analytical column, solved the problem. The whole operation is rather complex. Any mistake may cause the loss of resin. We documented every step including the disassembly of the equipment, the clean of the resin and the reinstallation of the analytical column. Experience in this period may benefit for the future work.