Abstract: The main modifications of a Type ZhT-1301 Mass Spectrometer intoType ZhT--1301G specially used for solid isotope, aud the measuring resultshave been reported in the present paper. By using the gas ion source withsingle beam method the precision is ±0.2%, the accuracy is ±0.5%; byusing the six bands-places solid source both precision and accuracy arebetter than 0.4%. Using 1 μg simple the intensity of ion current is 10~(-11) Aand can be stabilized for 4 hours or more.