Abstract: The measuremental accuracy is the most important specification for the TIMS . Especially, what is the main reason that long-term used TIMS has a bad accuracy is hard to judge. The most principle factores of the affecting measuremental accuracy and the method of how to overcome them were discussed in this paper. These methods consist of minimizing direction and energy divergences of the ion beam, increasing the stabilities of the electric and magnetic fields, correcting and exchanging of the multicollectores and electromultiplieres, using virtual amplifieres.