Abstract: Uranium isotope abundance ratio has been measured by total sample evaporation and signal integration,and a thermal surface ionization mass sepctrometry equipped with multicollector has been used.Total sample evaporation technique can eliminate the influence of mass fractionation,and accuracy measurement is directly achieved without calibration by isotope reference standard materials.Analysis software for total sample evaporation technique has been developed.The factors of interference measurement,such as sample size,signal intensity loss and sample residue,have been studied.Under 0.1～10 isotope ratio range and 95% confidence,the relative expanded uncertainty of the technique is 0.10%.